JPH0263273A - Focus control circuit - Google Patents

Abstract

PURPOSE:To quicken the accurate automatic focusing by discriminating the state as an unfocal state when a luminance component at a focus point just before and just after the detection of a focus point where the luminance component shows a maximum value is nearly equal to the maximum value and applying focus adjustment again. CONSTITUTION:A maximum value of a luminance component extracted by filter 5, 7 from an image pickup signal picked up by a CCD 2 is detected. Then a focus point where the luminance value showns a maximum value is detected and the focal state is obtained, then a central controller 10 detects it that the luminance component at the focus point just before and just after the focus position offering the maximum luminance component is nearly the same as the maximum value, the state is discriminated to be unfocal state and the focus adjustment is implemented again. Thus, the fluctuation of the focal point due to a rapid change or the like in the picked-up picture is surely detected and the accurate automatic focusing is implemented quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a contrast detection type focus control circuit suitable for use in, for example, an autofocus system of a video camera.

[Summary of the invention]

In a focus control circuit using a contrast detection method suitable for use in an autofocus system of a video camera, for example, the present invention detects a focus position of an in-focus point where a luminance component has a maximum value, and then detects a focus position where a luminance component has a maximum value. When it is detected that the brightness components at the focus position immediately before and after the focus point are approximately the same value as the maximum value at the focus point, it is determined that the focus is out of focus and the focus is adjusted again. This system is designed to reliably detect fluctuations in the focal point due to changes in focus, etc., and quickly perform accurate autofocus operations.

[Prior Art] Autofocus systems for video cameras can be categorized based on the principle of the focusing system: distance measurement systems and focus detection systems. The distance measurement method measures the distance to the subject and controls the position of the lens accordingly. The focus detection method detects the focus on the imaging surface and controls the position of the lens to the focused position.

One of the focus detection methods is the contrast detection method. The contrast detection method, as shown in Japanese Patent Application No. 62-146628, for example, performs focus control by utilizing the fact that the edges of the captured image become clearer as the lens approaches the in-focus position.

The fact that the edges of the captured image become clearer corresponds to the increase in high-frequency components in the video signal.

An autofocus circuit using such a contrast detection method determines the in-focus point, which is the position in focus.
This was done using the method shown below.

That is, for example, when detecting a focused point from the luminance signal in the photographed CIR signal, the integral value of the luminance signal level for one screen at multiple detection points set in advance on the inner surface is as shown in FIG. (, as the focused distance (focus position) of the imaging lens approaches the focal point (2 m in this example), it increases like a mountain, and once it passes this focal point, it decreases again. Therefore, this luminance signal level The integral value becomes the maximum value 2
It would be sufficient to detect m, but in reality, the focus ring of the imaging lens is slightly rotated back and forth from the 2 m position, and the integrated value y of the brightness level at the 2 m position is detected.

By detecting that is higher than the integral values y- and y+ of the luminance levels at the positions before and after this, it is detected that the focus position of 2 m is the maximum value. When the focus ring reaches 2m and is in focus through such detection work, the focus ring is periodically rotated slightly back and forth until the integrated value of the brightness level at the focus position before and after is the maximum value. As long as it continues to be detected that yo is not exceeded, it is determined that the camera is in focus, and imaging is maintained at this focus position.

For example, when the integral value of the brightness level for one screen at 2 m, which is the focal point, changes significantly, or when the integral value at the focus position immediately before or after 2 m exceeds the integral value at 2 m. When detected, it is determined that the focus position of the in-focus point has changed due to movement of the subject, etc., and the maximum value of the integrated value of the brightness level is detected again to search for the in-focus point.

[Problem to be solved by the invention]

However, when it is detected that the in-focus state continues in this way, it may be determined that the in-focus point has not changed, even though the focus position of the in-focus point has actually changed. Ta. For example, as shown in Fig. 3, when a curve y with a focused point of 2 m is detected and an image is taken at this 2 m focus position, the focused point suddenly changes to a curve X with a 4 m focus due to a change in the internal angle. Suppose that the brightness level shown is reached. At this time, since the integral value of the brightness level of the curve X is the same as that of the curve y at the focus position of 2 m, it is not possible to detect that the in-focus point has changed due to a change in the brightness level. In addition, this curve It was not possible to detect a change in the focal point even at the brightness level. For this reason, although good focus adjustment can actually be achieved by setting the imaging lens to a focus position of 4 m, the lens remains at a focus position of 2 m and does not move, resulting in an inconvenience that the captured image becomes out of focus.

SUMMARY OF THE INVENTION The present invention aims to provide a focus control circuit that can reliably detect fluctuations in the in-focus point.

[Means to solve the problem]

For example, as shown in FIG. 1, the focus control circuit of the present invention selects the filter (5), f? from the wi image signal captured by C0D (2). ) In a focus control circuit that performs focus control by detecting the maximum value of the brightness component extracted by When the central control device (10) detects that the luminance components at the focus positions immediately before and after are approximately the same value as the maximum value, it is determined to be an out-of-focus state and the freshness focus adjustment is performed. It is.

[Effect]

According to the focus control circuit of the present invention, when it is detected that the luminance components at the focus positions before and after the in-focus point are the luminance component at the in-focus point and the distance value, the brightness level near the in-focus point becomes flat. It is determined that this focus position may no longer be the focused point, and the focus adjustment operation is performed again to search for an accurate focused point.

〔Example〕

Hereinafter, one embodiment of the focus control circuit of the present invention will be described in the first embodiment.
Let's explain with reference to FIGS.

This example is a focus control circuit that is commonly used in the autofocus mechanism of a video camera, and Figure 1 shows the overall configuration. The image is formed on the imaging plane of a CCD type solid-state image sensor (hereinafter referred to as CCI) (2). In this case, the focus ring (1a) of the imaging lens (1) is rotationally driven by a motor (11), which will be described later, so that the focus position changes and the image light is focused on the imaging plane of C0D (2). Focus can be adjusted.

Then, the image signal output by the CCD (2) is supplied to the image signal processing circuit (3), which converts the image signal into a predetermined video signal, and converts the image signal into a predetermined video signal. is output from the output terminal (4).

Further, the baseband luminance signal component extracted from the fi1m signal by the imaging signal processing circuit (3) is supplied to a bypass filter (hereinafter referred to as HPF) (5). This website
F (5) is a filter that passes signals of 100 kHz or higher, and the output luminance signal of HP F (5) is supplied to a low-pass filter (hereinafter referred to as LPF) (7) via an amplification a (6). This L P F (?) is 2M
This is a filter that passes signals below Hz.

Then, the luminance signal output by this LPF (7) is converted into an analog signal into a digital signal.
After the digital signal is converted into a digital signal by the digital converter (8), it is supplied to the integrating circuit (9), and the integrating circuit (9) performs the integration process.In this case, the integrating circuit (9) is a digital integrating circuit, This is a circuit that integrates the brightness levels of all focus detection points of the brightness signal for one screen for each field. Note that a plurality of focus detection points in one screen are set in advance near the center of the screen. Then, the integral value data calculated by this integrating circuit (9) is converted into a centrally processed value!
! (hereinafter referred to as CPtJ) (10).

Then, the CPtJ (10) supplies a predetermined drive signal to the motor (11) for rotating the focus ring (1a) based on the result determined from the integral value data from the integration circuit (9), and performs focus adjustment. That's what I do.

In this case, the focus adjustment performed by the CPU (10) is as shown in the flowchart of FIG. Rotate 1a). Then, imaging is performed with this focus position as the in-focus point, but from then on, the focus ring (
1a) is sent to the motor (
11) to periodically detect integral value data at focus positions immediately before and after the focus position of the in-focus point. When the integral value data immediately before or after this exceeds the integral value data at the focus position that is the in-focus point, or when it is between the integral value data at the in-focus point and the integral value data, the in-focus point changes and is no longer at the apex. This is how I judge it. Furthermore, when the integral value data of the focus position that is the in-focus point changes significantly, it is determined that the in-focus point has changed, regardless of the previous and subsequent integral value data.

Next, the focus control operation performed by the focus control circuit of this example will be explained. First, the baseband luminance signal extracted by the imaging signal processing circuit (3) from the imaging signal output by the COD (2+) is transmitted to the LP F (
? ). For this reason, HPF [5
) and L P F (71) and 100 kHz from the luminance signal.
The signal components above 2MHz and below are extracted, and these 100
After the luminance signal component of ~2M Ilz is converted into a digital signal by an analog-to-digital converter (8), it is converted into a digital signal by an integrating circuit (9). Data of all focus detection points of the plane segment are integrated. The integral value in this case is, for example, if there is an imaging object at a distance of 2 m from the imaging plane of this video camera, and the distance to the focal point is 2 m, the imaging lens (11 focal points) as shown in FIG. -Casling (1a)
A curve characteristic y is obtained in which the integral value increases with the apex at a position at a distance of 2 m. Here, if it is assumed that the rotational position of the focus ring (1a) at the time of activation of this control circuit is a distance of 1 m, an integral value y1 is obtained in the CPU (10). At this time, the CPU (10) is connected to the motor (11).
The control signal is supplied to rotate the focus ring (1a) slightly in both directions, and the CPU ( 10) is determined. When this determination operation is completed, the focus ring (1a) is rotated under the control of the CPU (10) in the direction in which the integral value increases, that is, in the direction in which the distance of the focus position is lengthened. Maximum value at a distance of 2 m)F.

Detect that. At this time, the focus ring (la) once exceeds the distance 1i112 m and detects the integral value y2 that has slightly decreased from the maximum value of 7°, thereby determining that the integral value yo at the distance 1i112 m is the maximum value. C
The PU (10) makes the determination, determines that this 2m position is the in-focus point, and stops the focus ring (1a) at the 2m position.

In this example, this maximum integral value y.

After detecting, it is detected whether the in-focus state continues. That is, by rotating the focus ring (1δ) slightly back and forth at regular intervals, the integral value of the luminance component at the focus position immediately before and after is y.

The integral value decreased by 73! By detecting >'2, it is confirmed that the integral value yo at the distance MI 2 m is the maximum value, and it is determined that the in-focus state continues.

Assume that the integral value changes to a value represented by a characteristic X of a curve whose apex is when the focus ring (1a) is at a distance R4m, for example, due to movement of the subject currently being imaged. At this time, since the integral value x1 at the distance 1i1t 2 m is the same value as the maximum value yo of the characteristic y, it is not possible to detect a change in the in-focus point from a change in the level.

Therefore, the integral values x3 and x2 of the luminance component at the focus position immediately before and after the focus position are detected. This integral value X2,
3 is the integral value x1 at a distance of 2 m and the road distance value. For this reason, if the focus position at a distance of 2 m is no longer the vertex, C
The PU (10) makes a judgment and the CPU (10) controls the motor (1).
1) Supply a control signal to restart the focus ring (1a), perform an operation to search for the current maximum value XO, and after detecting the maximum value XO at a distance of M4m. , in the same way until a change in the focus point is detected.
The focus position of m is maintained.

In this way, according to the focus control circuit of this example, it is determined that the focal point is not in focus even when there is almost no change in the integral value, so that it can be reliably determined that the focal point has changed. For this reason, accurate autofocus operation is performed that quickly follows sudden changes in the focus point, such as when the detected value does not change even though the focus point changes due to sudden movement of the subject, etc. .

Note that the present invention is not limited to the above-described embodiments, and it goes without saying that various other configurations can be taken without departing from the gist of the present invention.

〔Effect of the invention〕

According to the focus control circuit of the present invention, shooting@! There is an advantage in that it is possible to reliably detect fluctuations in the in-focus point due to sudden changes in images, etc., and quickly perform accurate autofocus operations.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the focus control circuit of the present invention, FIG. 2 is a flowchart for explaining the example in FIG. 1, FIG. 3 is a characteristic diagram for explaining the example in FIG. FIG. 4 is a characteristic diagram for explaining the conventional autofocus operation. +11 is the imaging lens, (1a) is the focus ring, (
10) is a central processing unit.

Claims (1)

[Claims] In a focus control circuit that performs focus control by detecting the maximum value of the luminance component in an imaging signal, after detecting the focus position where the luminance component has the maximum value, the focus control circuit detects the focus position where the luminance component has the maximum value, and then performs focus control immediately before and after the focus position where the luminance component has the maximum value. A focus control circuit characterized in that when it is detected that a luminance component at a position is substantially the same value as the maximum value, it is determined that the focus is out of focus and the focus is adjusted again.