JPH04318772A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To drive the focus matching device with high accuracy even in a high brightness object by solving a problem of a fogged state when the brightness of the object is high in the automatic focus matching device configurated such that a high frequency component from a video signal is obtained from an image pickup element on a light receiving face of which the object image is formed and the focus matching device of a lens is driven to maximize the amplitude of the above frequency component. CONSTITUTION:The matching device is provided with a 2nd BPF 10 whose pass band frequency is higher and whose band width is narrower than those of a 1st BPF 5, and a high brightness detection circuit 12 detects it that an object has a higher brightness than that of a high frequency component and the detection signal is received by a 2nd control circuit 13 to select the two BPFs 5, 10, then even when the brightness of the object is high, the characteristic of the high frequency component is not an M-shape but an chevron, then the focus matching is correctly driven with high accuracy.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an automatic focusing device that detects high frequency components of a video signal from an image sensor of a video camera and drives a lens focusing device so that the amplitude of the high frequency components is maximized. be.

0002

2. Description of the Related Art In recent years, the demand for integrated video cameras has been rapidly increasing as they have become smaller and lighter. The automatic focusing device simplifies the handling of video-integrated cameras and contributes to their further widespread use.

A conventional automatic focusing device will be explained below. FIG. 3 shows a block diagram of a conventional automatic focusing device. In FIG. 3, 1 is a lens, 2 is an image sensor that converts the object imaged on the imaging surface into an electrical signal, 3 is a preamplifier that amplifies the output of the image sensor 2, and 4 is a preamplifier that amplifies the output of the image sensor 2.
5 is a process circuit that processes the video signal output from the preamplifier 3 and converts it into a television signal, and 5 is a band pass filter (hereinafter referred to as BPF) that detects high frequency components from the video signal obtained by the image sensor 2. ), for example, 30
It has a 0Hz to 3MHz passband. 6 is a reference frequency component detector that detects a reference frequency component included in the high frequency component obtained by the BPF 5; 7 is a motor drive circuit that controls the lens 1 so that the amplitude of the high frequency component is maximized; 8 and a motor 9 to slightly vibrate the focusing device of the lens 1 at a reference frequency.

The operation of the conventional automatic focusing device configured as described above will be explained below.

The motor 9 uses the reference frequency supplied from the control circuit 7 to slightly move the focusing device of the lens 1 to change the focus of the lens 1 to an extent that cannot be detected by the eye. As a result, the high frequency component included in the output signal of the image sensor 2 undergoes amplitude fluctuations at the reference frequency and has a reference frequency component. The high frequency component is detected by the BPF 5, and the reference frequency component included therein due to focus change is detected by the reference frequency component circuit 6. The signal is sent to the control circuit 7
The polarity and amplitude are detected in the motor drive circuit 8 and the motor 9.
The focusing device of the lens 1 is driven so that the high frequency component of the output signal of the image sensor 2 is maximized.

The principle of detecting the driving method of the motor 9 will be explained in more detail with reference to FIG. The vertical axis is the amplitude of the high frequency component included in the output signal of the image sensor 2,
The horizontal axis is the position of the focusing device of the lens 1. Near is a position that focuses on a nearby subject, and far is a position that focuses on a distant subject. Now, if we consider the case where an image of a subject at a distance D1 is taken, the focusing device of the lens 1 is set at the distance D1.
When it is at a position corresponding to 1, it is in focus and the amplitude of the high frequency component is maximum. Even if the focusing device is shifted closer or further away from the above-mentioned position, the amplitude of the high frequency component decreases, resulting in a kind of chevron-shaped characteristic as shown in A shown in FIG. 2. On the other hand, a1, a2, and a3 indicate movements of the focusing device due to fine movements of the motor 9 at the reference frequency at each lens position. Due to the change in focus accompanying the slight fluctuation shown in a1, the high frequency component undergoes amplitude modulation as shown in b1 and has a reference frequency component. Further, the slight fluctuation shown in a2 undergoes amplitude modulation shown in b2. The amplitude modulation is b
As is clear from 1 and b2, the phase is reversed by 180 degrees between the near and far sides of the in-focus position. Therefore, a reference frequency component is detected from high frequency components subjected to amplitude modulation such as b1, and the reference frequency component is synchronously detected with the reference frequency to detect the amplitude and phase of the component. If the motor 9 drives the focusing device of the lens 1 in the direction of the arrow c1 using the detection signal, then in the case of b2, it will be driven in the direction of the arrow c2. Therefore, the motor 9 always drives the focusing device to the position where the high frequency component is maximum, and a focused state is obtained. As described above, this conventional automatic focusing device has many features such as being able to form a closed loop including the lens focusing device, and making it possible to assemble the focusing device in a rough manner.

[0007]

However, the above conventional configuration has the following problems. When the lens position moves away from the in-focus point, the image of the subject captured on the image sensor 2 has two properties: one is that the contrast decreases, and the other is that the image becomes larger. Further, when the contrast decreases, the high frequency components become small, and when the image becomes large, the high frequency components become large. For normal subjects, when the subject moves away from the focal point, the contrast decreases more than the image gets larger, and the high frequency components become smaller, resulting in a chevron-shaped waveform like A in Figure 2. In the case of high brightness, the property that the image becomes large and the high frequency components become large appears largely near the focal point, resulting in an M-shaped waveform as shown in B shown in FIG. Since the automatic focusing device operates so that the amplitude of high-frequency components is maximized, the lens is driven to the e1 or e2 position for a high-brightness object, creating a blurred television signal.

The present invention solves the above-mentioned conventional problems, and aims to provide an automatic focusing device that can reliably focus even a high-brightness object.

[0009]

[Means for Solving the Problems] In order to achieve this object, the automatic focusing device of the present invention detects high frequency components from a video signal obtained from an image sensor that forms a subject image on an imaging surface, The lens focusing device is configured to drive so that the amplitude of the high frequency component is maximized, and when the subject is of high brightness, the configuration is such that the band in which the high frequency component is detected can be changed. .

0010

[Effect] For high-brightness objects, when the lens moves away from the focal point, the effect of the image becoming larger is greater than the property that the contrast decreases, and the high-frequency components exhibit M-type characteristics, but the high-frequency components are detected. By changing the frequency band and detecting only higher frequency components, the influence of the above two properties is reversed, so even a high-brightness subject can be reliably focused.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

[0012] In FIG. 1, the same components as those in the conventional configuration are given the same numbers and their explanations are omitted. However, B
The PF5 is expressed as a first BPF5, and the control circuit 7 is expressed as a first control circuit 7. A second BPF 10 has a higher passband frequency and narrower bandwidth than the first BPF 5, and has a passband of 1 MHz to 3 MHz, for example. Reference numeral 11 denotes a switching circuit for switching between the first BPF 5 and the second BPF 10, and the second BPF 10 is selected by the second control circuit 13 when the subject is of high brightness. The high-brightness detection circuit 12 is a circuit that detects that the subject is high-brightness based on high frequency components.

The operation of the automatic focusing device of this embodiment constructed as described above will be explained with reference to FIG.

[0014] When the position of the lens moves away from the focal point D1, the image of the subject captured on the image sensor has two properties: one is that the contrast decreases, and the other is that the image becomes larger. Further, when the contrast decreases, the high frequency components become small, and when the image becomes large, the high frequency components become large. For normal subjects, when the subject moves away from the in-focus point, the contrast decreases more than the image gets larger, and the high frequency components become smaller, resulting in a chevron-shaped waveform like A in Figure 2. In the case of brightness, the property that the image becomes larger and the high-frequency components become larger appears largely near the focal point, resulting in an M-type waveform as shown in B shown in FIG. Since the automatic focusing device operates so that the amplitude of the high frequency component is maximized, the lens is driven to the position e1 or e2 in the case of a high-brightness object. However, if you change the band for detecting high frequency components and detect only the higher frequency components, the influence of the above two properties will be reversed, and the image will become larger and the higher frequency components will become larger. The effect of the property that the contrast decreases and the high frequency components become smaller increases. Therefore, the waveform of the high frequency component for a high-brightness subject becomes as shown in A shown in FIG. 2, and even for a high-brightness subject, an in-focus state can be obtained reliably.

As described above, according to this embodiment, the subject image formed on the light-receiving surface of the image sensor 2 is periodically and optically blurred, and the high frequency of the video signal obtained from the image sensor 2 is component, detects a signal corresponding to the blur from the detection signal, and drives a focusing device of the lens 1 so that the amplitude of the high frequency component is maximized. By increasing the frequency at which the high-frequency component is detected and narrowing the band, the accuracy during focusing can be greatly improved and the operating range of the system can be expanded to even higher brightness. Alternatively, the means for detecting that the object is of high brightness may be one that detects the level of the video signal and determines that the object is of high brightness when the level reaches a certain value.

[0016]

[Effects of the Invention] The automatic focusing device of the present invention detects a high frequency component from a video signal obtained from an image sensor in which a subject image is formed on a light receiving surface, and maximizes the amplitude of the high frequency component. In a system that drives a lens focusing device to achieve high brightness, focusing accuracy can be greatly improved by narrowing the band for detecting the high frequency component or changing the detection frequency when the subject is of high brightness. can be improved to
It can magnify even higher-brightness objects, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic focusing device in an embodiment of the present invention.

[Figure 2] Characteristic diagram for explaining the principle of detecting the driving direction of the motor

[Figure 3] Block diagram of a conventional automatic focusing device

[Explanation of symbols]

1 Lens 2 Imaging device 3 Preamplifier 4 Process circuit 5 First bandpass filter 6 Reference frequency component detection circuit 7 First control circuit 8 Motor drive circuit 9 Motor 10 Second bandpass filter 11 Switching circuit 12 High brightness detection circuit 13 Second control circuit

Claims (1)

[Claims] 1. An image sensor that converts an object imaged on an image sensor into an electrical signal, a lens for focusing the image sensor, a preamplifier that amplifies the output of the image sensor, and a preamplifier that amplifies the output of the image sensor. a process circuit that processes the video signal that is the output of the preamplifier and converts it into a television signal; a plurality of bandpass filters that detect different high frequency components from the video signal obtained by the image sensor; a switching circuit for switching the band-pass filter; a reference frequency component detector for detecting a reference frequency component included in the high-frequency components obtained by the band-pass filter; a first control circuit that controls the lens and slightly vibrates the lens at a reference frequency using a motor drive circuit and a motor; a high-brightness detection circuit that detects a high-brightness object from the video signal; and a second control circuit for switching the plurality of bandpass filters based on the obtained high-intensity detection signal.