JPH0433480A - Automatic focus device - Google Patents

Abstract

PURPOSE:To surely attain focus adjustment without causing a delay in the focus speed by delaying a line in a focus area, taking a difference between the delayed data and a data not delayed and integrating the result. CONSTITUTION:An area gate 4 extracts a luminance signal from a video signal processing circuit 3 to extract a luminance signal in a focus area and the luminance signal is delayed by a time (1H+alpha) (alpha is a minute time smaller than 1H) with a delay line 5 and a differential amplifier 6 detects a difference between the delayed luminance signal and the luminance signal not delayed. The difference is converted into an absolute value by an absolute value circuit 7 and the output of the absolute value circuit 7 is A/D-converted and led to an integration circuit 9. Since scanning is implemented in an oblique direction, no confusion is caused in the focusing in any direction. Thus, the accurate focus adjustment with simplified circuit constitution is implemented without slowing down the focus speed.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is an autofocus device installed in a video camera, an electronic still camera, etc., and more specifically, an improvement has been made in consideration of the simplification of the autofocus circuit. The present invention relates to an autofocus device.

(Prior Art) Autofocus devices focus by extracting high frequency components and the like using the output of an image sensor such as a CCD, and have advantages and disadvantages depending on the scanning direction for focusing.

Conventional AF systems generally only evaluate level changes in the horizontal direction and do not evaluate level changes in the vertical direction.

FIG. 3 shows an example of a subject that is difficult to focus on when scanning in the vertical and horizontal directions.

As shown in (b), the horizontal scanning is delayed by a minute time α and the difference is detected.

Therefore, although it is possible to reliably focus on the subject in (a), it is difficult to focus on the subject in (C).

Also, as for vertical scanning, 1 as shown at +dl.
Since the difference is detected with a delay of H, contrary to the above, the subject in (C) can be reliably focused, but
), it was extremely difficult to focus.

Therefore, there has been a need for something that can reliably perform focus adjustment even when a large amount of DC components are included in any direction of the subject.

Traditionally, the horizontal direction was used to meet this request.

There were devices that detected and synthesized level changes in each vertical direction (Japanese Patent Application Laid-Open No. 62-38083, Japanese Patent Application Laid-open No. 60-9)
No. 7784).

In addition, as another example, there was a system in which focus detection signals are extracted using a horizontal HPF and a vertical HPF, and one of them is selected for determination (Japanese Patent Application Laid-open No. 199174/1983).

(Problem to be Solved by the Invention) However, in the former example, a delay line is required in each of the horizontal and vertical directions, so a circuit for focus detection must be provided correspondingly, and the circuit configuration The disadvantage is that it becomes complicated.

Furthermore, the latter example requires multiple distance measurement operations, which causes a decrease in focusing speed.

The object of the present invention is to solve each of the above-mentioned drawbacks, and to solve the above-mentioned problems, it is an object of the present invention to solve the above-mentioned problems.
To provide an autofocus device that can perform accurate focus adjustment regardless of horizontal stripes.

(Means for Solving the Problems) In order to achieve the above object, an autofocus device according to the present invention detects a focus state from a video signal obtained from an image sensor, and drives a lens based on the detected focus signal. A video signal processing circuit that processes the output of the image sensor and outputs a video signal in an autofocus device that performs focusing, and an area gate that extracts a signal within the focus area from the luminance signal from the video signal processing circuit. , a delay element that delays the extracted luminance signal by (1H minute time α), a difference circuit that outputs the difference between the output of the delay element and the area gate output, and an absolute value of the output of the difference circuit. It is composed of an absolute value conversion circuit that outputs an output, an integration circuit that integrates the output of the absolute value conversion circuit, and an AF control circuit that drives and controls the lens so that the output of the integration circuit becomes maximum.

(Example) Hereinafter, the present invention will be explained in more detail with reference to the drawings.

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

Light incident from an object (not shown) is imaged by a lens 1 onto an image sensor 2 surface.

The output of the image sensor 2 is guided to a video signal processing circuit 3, where a synchronization signal and the like are added, and the video signal processing circuit 3 outputs a video signal.

The area gate 4 takes out the luminance signal from the video signal processing circuit 3 and extracts the luminance signal of the focus area.

The extracted luminance signal is transmitted through the delay line 5 to 1H0α (1H
is delayed by an infinitesimal amount of time).

The difference circuit 6 detects the difference between the luminance signal delayed by 1H+α and the undelayed luminance signal.

As shown in FIG. 2, this difference is the difference between the intersections of each 1H line and a diagonal line whose slope is determined by the ratio of the distance on the 1H line corresponding to the minute time α to the distance between the lines. Specifically, it becomes AB, BCl...

This difference is converted into an absolute value by the absolute value conversion circuit 7. The output of the absolute value converting circuit 7 is then A/D converted and guided to the integrating circuit 9.

The integrating circuit 9 integrates the magnitude of the difference within the focus area and averages it.

The AF control circuit 10 receives the averaged value and controls the lens drive circuit 11 so that the integrated value is maximized. A lens drive circuit 11 moves the lens 1 forward or backward to bring it to a focused point.

Since the present invention performs scanning in an oblique direction, there is no confusion in focusing operation in any direction.

(Effects of the Invention) As explained above, according to the present invention, the line in the focus area is delayed by 1H+α, the difference between this delayed data and the non-delayed data is taken, and then integrated. Therefore, instead of using a complicated circuit configuration in which a delay line and a detection circuit are provided in the horizontal and vertical directions, a simple circuit configuration consisting of one delay line and a detection circuit can be used in both the horizontal and vertical directions. It is possible to provide an autofocus device that can reliably perform a focus adjustment operation without causing a delay in focusing speed even if a direction contains a large amount of DC component.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an autofocus device according to the present invention, FIG. 2 is a diagram for explaining a diagonal scanning point according to the present invention, and FIG. 3 is a diagram for explaining a conventional method. In the figure, (al and (C1) are examples of subjects with vertical and horizontal striped patterns. Tbl and (dl in the same figure indicate scanning points in the horizontal and vertical directions, respectively. 1... Lens 2...・Image sensor 3 ・Video signal processing circuit 4 ・Area gate 5 ・(LH+α) delay line 6 ・Differential circuit 7 ・Absolute value conversion circuit 8 ・A/D conversion circuit 9... Integrating circuit 10... AF control circuit 11... Lens drive circuit

Claims (1)

[Claims] Detects the focus state from the video signal obtained from the image sensor,
An autofocus device that performs focusing by driving a lens based on the detected focus signal includes a video signal processing circuit that processes the output of the image sensor and outputs a video signal, and a luminance signal from the video signal processing circuit. Among them, there is an area gate that extracts the signal within the focus area, and an area gate that extracts the signal within the focus area, and a
), a difference circuit that outputs the difference between the output of the delay element and the area gate output, an absolute value conversion circuit that outputs the absolute value of the output of the difference circuit, and an output of the absolute value conversion circuit. an integrating circuit that integrates; and an AF that drives and controls the lens so that the output of the integrating circuit is maximized;
An autofocus device comprising a control circuit.