JPH02111178A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To prevent sensitive reply to an information change specific to a moving picture or to noise by averaging information being a basis of focus control of a pickup lens in advance. CONSTITUTION:An output of an image pickup element 14 is amplified by an amplifier 16 and converted into a usual video signal by a conversion circuit 18. An HPF 20 extracts a high frequency component from an output of the conversion circuit 18 and applies the result to an averaging circuit 29. The output of the HPF 20 is multiplied by I/N at a coefficient circuit 22 and applies to a lens control circuit 30 via an adder 24. Thus, the signal of the existing field and a signal of a preceding field are added in a rate of 1:N-1 and averaged. The lens control circuit 30 uses the averaged signal to regulate the focus of a lens unit 12 according to the known automatic focus system. Thus, the device is not disturbed due to disturbance of noise or a faulty signal of moving picture information.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an automatic focusing device, and more specifically to an automatic focusing device.
This invention relates to an automatic focusing device for a camera.

[Conventional technology]

2. Description of the Related Art Autofocus devices for video cameras that automatically control the lens position of the camera based on a video signal obtained from an image sensor are well known. For example, a method is known in which only the high frequency components of the video signal are extracted and the camera lens is controlled so that the high frequency components are maximized.

[Problem to be solved by the invention]

However, in the conventional example described above, the high frequency components to be extracted often increase or decrease more than necessary due to noise superimposed in the signal transmission system or changes in video information specific to moving images, which is one of the factors that cause errors in automatic focusing operation. Ta.

Therefore, it is an object of the present invention to provide an automatic focusing device for a video camera that does not cause such malfunctions.

[Means to solve the problem]

The automatic focusing device according to the present invention includes means for forming a focus signal indicating a focus state of a photographing optical system from an imaging signal, an averaging means for averaging the focus signal among a plurality of screens, and an averaging means for averaging the focus signal between a plurality of screens. It is characterized by comprising a control means for controlling the focusing of the photographing optical system using the output of the means.

[Effect]

By providing the above-mentioned averaging means, it is possible to prevent focus control from being adversely affected by fluctuations in focus signals between screens and noise.

〔Example〕

The present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. 1
0 is a subject, 12 is a lens unit, 14 is an image sensor, 16 is an amplifier, 18 is a conversion circuit that converts the output of the amplifier 16 into a video signal, and 20 is a high bus filter (H
PF), 22 is a coefficient circuit that multiplies the output of the HPF 20 by L/N (N is a constant), 24 is an adder, and 26 is a delay that delays the human input signal by one vertical interval period by sampling it for each field. 28 is a coefficient circuit that multiplies by (N-1)/N, and 30 is a lens control circuit that automatically adjusts the focus of the lens unit 12. The coefficient circuit 22, the adder 24, the delay circuit 26, and the coefficient circuit 28 constitute a cyclic averaging circuit 29, and the constant N is selected so that the sensitivity of the lens control circuit 30 is optimized.

A subject image formed on the image sensor 14 by the L lens unit 12 is converted into an electrical signal there.

The output of the image sensor 14 is amplified by an amplifier 16 and converted to a normal video signal by a conversion circuit 18. HPF2
0 extracts high frequency components from the output of the conversion circuit 18,
It is applied to the averaging circuit 29 (ie, the coefficient circuit 22).

The output of the HPF 20 is multiplied by 1/N by the coefficient circuit 22 and applied to the lens control circuit 30 via the adder 24. The output of adder 24 is transmitted to delay circuit 26 for one vertical interval period, i.e. 1
It is delayed by one field, and the coefficient circuit 28 calculates (1-N)/N.
After being multiplied, it is applied to the adder circuit 24 again.

Through this loop, the signal of the current field and the signal of the previous field are added and averaged at a ratio of 1:N-1.

Lens control circuit 30 uses the above averaged signal to adjust the focus of lens unit 12 according to a known autofocus method. This averaged signal is stable over time, and the lens control circuit 30 can operate the lens unit (12) without being disturbed by noise or abnormal signal disturbance of video information.
can be controlled.

In the embodiment shown in FIG. 1, the averaging circuit 29 is constructed by hardware, but of course it can also be implemented by a program using a microcomputer or the like. FIG. 2 shows a flowchart corresponding to the averaging circuit 29 portion. First, wait for vertical synchronization signal V 5sync (Sl)
, when the vertical synchronization signal is input, the output of HPF18 is
/D conversion, import (S2), and store in variable X (S
3). Then, an averaging operation is performed (S4). Y is the current average value and Yl is the average value one vertical interval ago. For averaging in the next field, Yl is updated by Y (S5), and the degree of focus is determined by the value of Y.
A control signal is output to the lens control circuit 30 (S7). This drives the lens into focus (S8).

After this, return to Sl and repeat the above operation.

In the above embodiment, for ease of explanation, the high frequency components of the image are sampled every vertical interval and averaged. It goes without saying that different sampling periods and averaging techniques may be used.

〔Effect of the invention〕

As can be easily understood from the above explanation, according to the present invention, the information that is the basis for focusing control of the photographic lens is averaged in advance, so that it is not possible to respond too sensitively to noise and changes in information specific to moving images. This makes it possible to perform smooth focusing control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, and FIG. 2 is a flowchart of a program that implements the function of the averaging circuit 29 shown in FIG. 10-...Subject 12...Lens unit 14
...-Image sensor 16--Amplifier 18--Conversion circuit
20--High pass filter 22, 2L--Coefficient circuit 24--Adder 26--Delay circuit 29-Averaging circuit 30--Lens control circuit Fig.

Claims (1)

[Claims] means for forming a focus signal indicating the focusing state of the photographing optical system from the imaging signal; an averaging means for averaging the focus signal among a plurality of screens; An automatic focusing device comprising: a control means for controlling focusing.