JP2869086B2 - Imaging device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as a video camera having a viewfinder and a focus control unit, and in particular, to a display for displaying the degree of focus of a subject on the viewfinder. Regarding the mechanism.

(B) Conventional technology Generally, a video camera uses a manual focus control mechanism for manually moving a focus lens in the optical axis direction to perform focus control, and a distance measurement method using infrared rays or a high-frequency component of a luminance signal. In many cases, an automatic focus control mechanism that automatically advances and retracts the focus lens based on the AF information obtained from the AF sensor using the TTL method has been adopted.

When the above-described manual focus control is executed, the focus is affected by the diopter, and it is difficult to find a focal point when the depth of field is large, such as at a wide angle.

Therefore, for example, JP-A-62-84660 (HO4N5 / 232)
As described above, it is always determined whether or not the camera is in focus based on the AF information required during autofocus control, and when it is determined that the camera is in focus, the light emitting element is turned on, and the user is also notified during manual focus control. A method of notifying that the focus has been reached has been proposed.

(C) Problems to be Solved by the Invention According to the related art, the display by the light emitting element merely indicates the result of determining whether or not the in-focus state has been reached. The user does not know at all about the degree of focusing, that is, whether or not the subject is quite close to the image, that is, the degree of focusing.

(D) Means for Solving the Problems The present invention provides a first filter for extracting a high-frequency component of an imaged video signal, a cutoff frequency lower than the first filter, and a high-frequency component of the imaged video signal. A second filter for extracting the component, a first integration for integrating the output of the first filter for a predetermined period to obtain a first integration value, and an integration of the output of the second filter for a predetermined period to obtain a second integration value A second integration means; and a detection means for calculating a ratio of the first integration value to the second integration value and detecting a degree of focus of the subject, and displaying the degree of focus on a viewfinder. .

(E) Function Since the present invention is configured as described above, accurate focusing can be quickly performed even during manual focus control.

(F) Example Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit block diagram of an embodiment of the present invention. In the figure, (1) is a focus lens, (2) is an imaging circuit having an imaging device, (3) is a gate circuit for setting a focus area, (4) is a synchronization separation circuit, (5) is a timing generation circuit, 12a) and (12b) are bandpass filters (BP
F), (13a) and (13b) are detection circuits, (14a) and (14b) are digital integration circuits, (10) is an electronic viewfinder,
(11) is a focus information display circuit, and (21) is focus control means for controlling the advance / retreat of the focus lens (1) in the optical axis direction to perform a focusing operation.

Light from the subject is focused on the image sensor (2) via the focus lens (1), and is output as a captured video signal. This captured video signal is supplied to a gate circuit (3), a synchronization separation circuit (4), and a focus information display circuit (9).

A sync separation circuit (4) separates a vertical synchronizing signal and a horizontal synchronizing signal from an imaged video signal, and a timing generating circuit (5) outputs a fixed oscillator output used for driving both the synchronizing signal and the image sensor (2). FIG. 2 (a)
As shown in (b), a rectangular sampling area, that is, a focus area (30) is set in the center portion of the screen, and a gate opening / closing signal that allows the passage of a luminance signal in an imaged video signal only within the focus area is provided by a gate circuit. Supply to (3). In this way, only the luminance signal corresponding to the area within the focus area is time-divided by the gate circuit (3).
F (12a) and (12b).

The BPF (12a) extracts only the high frequency components from 600 KHz to 2.4 MHz as shown in FIG. 3 (a), and the BPF (12b)
200K including lower frequency components than BPF (12a) as shown in Fig. (B)
It has a cutoff frequency of HZ to 2.4MHZ.

The BPF (12a) (12b) outputs are output from the detection circuits (13a) (13
After the amplitude detection in b), the digital integrator (14a)
At (14b), digital integration is performed for one field. Here, digital integrators (14a) (14b)
Has an A / D converter for A / D converting the detection output and an adder (not shown), and outputs an integrated value every time integration over one field period is completed. Thus, as described above, the BPF (12
a) The integral values (M) and (N) for one field of each high-frequency component of the luminance signal whose band is specified in (12b) are input to an arithmetic circuit (focus degree detecting means) (15).

The arithmetic circuit (15) calculates an integral value (M) for the integral value (N).
Is calculated as a relative ratio (R) (R = M / N). Meanwhile, the relationship between the integral values (M) and (N) and the lens position is a characteristic curve as shown in FIG. That is, the integral value (M) for the high frequency component of 600 KHZ or more becomes a curve showing a steep change near the focal point, and the integral value (N) including the low frequency component is slower than the integral value (M). Curve, but always N> M
Holds, the focus shifts as the distance from the focal point increases, and the attenuation starts from a component having a high spatial frequency of the subject, so that a large difference occurs between the integral values (M) and (N).

A graph showing the relationship between the relative ratio (R) and the degree of blurring of the subject (the amount of deviation from the focal point) is a monotonically decreasing characteristic curve as shown in FIG. This is because the state amount of the relative ratio is the in-focus state of the subject (the degree of blur or the focal point).
Is a function value that can be expressed as a ratio, and is a kind of normalized state quantity because it is expressed as a ratio, indicating that it has a property that is hardly affected by the environment where the subject is placed. For example, when the illuminance of the subject changes, the integral value itself changes, but the relative ratio (R) does not change much. Usually, since the above-mentioned properties are not limited to the type of the subject, this relative ratio can be used as a parameter of the degree of blur. As described above, the relative ratio (R)
Is a state quantity representing the degree of blur or the degree of focus, the arithmetic circuit (15) supplies this relative ratio (R) to the focus information display circuit (11).

The focus information display circuit (11) superimposes the relative ratio (R), which is a digital value, on the captured video signal using a character generator in the form of%, and outputs
On-screen display is performed on the viewfinder (10) as shown in FIGS. FIG. 9 (a) shows that the relative ratio (R) is 0.
32 indicates that the camera is out of focus, and FIG.
= 0.90, indicating that the camera is in a substantially focused state. Therefore,
The user only has to execute the manual focus control using the relative ratio (R) as a guide.

As the focus information display circuit (11), a focus indicator (31) may be displayed in the captured video signal using a character generator as shown in FIGS. 2 (a) and 2 (b). Alternatively, it is also possible to use an LED, an LCD, or the like arranged in the same field of view as the CRT in the viewfinder (10).

It is needless to say that the relative ratio (R) can be used as a parameter for drive control of the focus motor as the degree of out-of-focus during the autofocus control.

In this embodiment, the upper limit of the cutoff frequency of the BPFs (12a) and (12b), which is 2.4 MHZ, is set sufficiently higher than the band that the luminance signal can take.

(G) Effects of the Invention As described above, according to the present invention, quick and accurate focus control can be performed by recognizing the degree of focus that is not easily affected by the environment where the subject is placed while looking at the screen on the viewfinder. It becomes possible.

[Brief description of the drawings]

1 to 6 relate to an embodiment of the present invention. FIG. 1 is a circuit block diagram, FIGS. 2 (a) and 2 (b) are views showing a screen on a viewfinder, and FIGS. 3 (a) and 3 (a). b) is a characteristic diagram of the BPF, FIG. 4 is a graph showing the relationship between the lens position and the integrated value, FIG. 5 is a graph showing the relationship between the degree of blur and the relative ratio, and FIGS. It is a figure showing a screen. (10) Viewfinder, (21) Focus control means, (12a) (12b) Bandpass filter, (14a) (14)
b)… digital integrator, (15)… arithmetic circuit (focusing degree detecting means).

Claims (1)

(57) [Claims] 1. A viewfinder for projecting an image screen, focus control means for performing focus control on a subject, first filter means for extracting a high-frequency component of an image signal, and lower than the first filter means. A second filter having a cutoff frequency and extracting a high-frequency component of the captured video signal; a first integrating means for integrating the output of the first filter for a predetermined period to obtain a first integrated value; Integrating the output of the filter means for the predetermined period,
A second integrating means for obtaining an integrated value; and a detecting means for calculating a ratio of the first integrated value to the second integrated value to detect a degree of focus of the subject, and displaying the degree of focus on the viewfinder. An imaging device, comprising: