JP2748425B2 - Video camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera equipped with a contrast detection type focus control circuit suitable for application to an autofocus system.

[Summary of the Invention]

The present invention relates to a video camera provided with a focus control circuit of a contrast detection method suitable for application to an autofocus system, wherein an integrated value of a signal in a predetermined first frequency band extracted from a luminance component in an image pickup signal After the focus control is performed so that the maximum value becomes the maximum value, it is periodically determined at predetermined intervals whether or not the integrated value of the luminance component of the second frequency band in the first frequency band exceeds a predetermined focus determination level. In the focus control circuit configured to detect and perform the focus determination, it is determined that the integrated value of the luminance component of the second frequency band has exceeded the focus determination level at least once within a plurality of predetermined detections. When it is detected, it is determined that the camera is in focus, and the autofocus operation is stably performed even when the camera is vibrating due to camera shake or the like.

[Conventional technology]

The video camera's autofocus method includes a distance measurement method and a focus detection method when classified based on the principle of the focusing method. The distance measuring method measures the distance to a subject and controls the position of a lens in accordance with the distance. The focus detection method detects focus on an imaging surface and controls the position of a lens at a position where focus is achieved.

One of the focus detection methods is a contrast detection method. In the contrast detection method, as shown in Japanese Patent Application No. 62-146628, for example, focus control is performed by utilizing the fact that the edge of a captured image becomes clearer as the lens approaches a focusing position. The sharpening of the edge of the captured image corresponds to an increase in the high frequency component in the video signal.

In the autofocus circuit based on such a contrast detection method, the determination of the in-focus point which is the in-focus position is performed by the following method. That is, for example, when the focus point is detected from the luminance signal in the imaging signal, one of the luminance signal bells at a plurality of detection points set in advance on the screen.
As shown in FIG. 3, the integral value of the screen increases in a mountainous manner as the focused distance (focus position) of the imaging lens approaches the focal point (2 m in this example). Decrease again. For this reason, it is only necessary to detect 2 m at which the integrated value of the luminance signal level becomes the maximum value.However, in practice, the focus ring of the imaging lens is slightly rotated back and forth from the 2 m position to move the focus ring to the 2 m position. The maximum value is detected by detecting that the integrated value y ₀ of the luminance level is higher than the integrated values y ₋ and y ₊ of the luminance levels at the positions before and after this.

[Problems to be solved by the invention]

By the way, such an autofocus circuit has a disadvantage that it does not operate well when the video camera is vibrated due to hand shake or the like. That is, when the video camera is stationary, it is assumed that a luminance component having a frequency characteristic indicated by a curve x in FIG. 4 is obtained from the image pickup signal, for example. In this case, it is assumed that there is a luminance peak near 1 MHz, for example. At this time, since the contrast of the image pickup signal of the same subject imaged in a state where the video camera is moved due to camera shake decreases, the luminance component of the image pickup signal in this camera shake state is 1 MHz as shown by a curve x 'in FIG. There is no nearby high frequency component, resulting in signal characteristics having a peak in the low frequency range. For this reason, in a state where camera shake occurs, the above-described integrated value of the luminance level becomes a value in which the contrast is different from that in a state where the camera is still, and the focus control circuit malfunctions, and the focus position of the imaging lens is out of focus. .

In view of the above, an object of the present invention is to provide a contrast detection type focus control circuit that can stably detect a focal point when a camera is vibrating due to camera shake or the like.

[Means for solving the problem]

The video camera of the present invention is, for example, as shown in FIG.
The first high-pass filter (6
After the central control unit (12) performs focus control so that the integration value of the signal of the first frequency band extracted by the a) and the low-pass filter (9) by the integration circuit (11) becomes the maximum value, The integration value of the luminance component of the second frequency band determined by the second high-pass filter (6b) and the low-pass filter (9) by the integration circuit (11) exceeds a predetermined focus determination level periodically at predetermined intervals. In the focus control circuit in which the central control device (12) performs the focus determination, the focus control circuit (12) performs the focus determination once or more when the integrated value of the luminance component of the second frequency band is detected, for example, ten times. When the central controller (12) detects that the level has been exceeded, it is determined that the camera is in a focused state.

[Action]

According to the video camera of the present invention, the integral value of the luminance component in the narrow second frequency band determined by the second high-pass filter (6b) and the low-pass filter (9) is different from that of the other non-focus only near the focal point. The signal is higher by a predetermined level than when in the in-focus range. Therefore, by detecting whether or not the integrated value of the second frequency band is higher by a predetermined level, it can be determined whether or not the in-focus state is continued. In this case, when the camera is moving due to vibration due to camera shake or the like, the camera moves substantially periodically, so that the state in which the camera is stationary and the state in which the camera is moving are substantially periodically repeated. Therefore, the integral value of the luminance component of the second frequency band detected in a vibrated state can be obtained by detecting a plurality of times, such as 10 times.
At least once, a value in a state where the camera is substantially stationary is detected. If the value at this time is higher by a predetermined level, it can be determined that the in-focus state is continued.

〔Example〕

Hereinafter, an embodiment of the video camera of the present invention will be described with reference to FIGS.
This will be described with reference to FIG.

This example is a focus control circuit applied to an auto-focus mechanism of a video camera, and FIG. 1 shows an overall configuration. In FIG. 1, (1) shows an imaging lens, and the image light passing through the imaging lens (1) is a CCD type solid-state imaging device (hereinafter referred to as C).
An image is formed on the image plane of (2). In this case, the focus adjustment of the image light formed on the image forming surface of the CCD (2) is performed by rotating the focus ring (1a) of the imaging lens (1) with the motor (13) described later.

An imaging signal output by the CCD (2) by imaging is supplied to an imaging signal processing circuit (4) via an imaging signal amplifier (3), and the imaging signal processing circuit (4) converts the imaging signal to a predetermined signal. It is converted into a video signal, and this video signal is output from the output terminal (5). In this case, the gain of the imaging signal amplifier (3) is automatically adjusted by gain adjustment data output according to the imaging signal level detected by the imaging signal processing circuit (4), and is supplied to the imaging signal processing circuit (4). Is controlled so that the level of the imaging signal is constant.

The baseband luminance signal component extracted from the imaging signal by the imaging signal processing circuit (4) is supplied to a first high-pass filter (hereinafter, referred to as HPF) (6a) and a second HPF (6b). The first HPF (6a) is a filter that passes signals of 100 kHz or more, and the second HPF (6b) is a filter that passes signals of 1 MHz or more. And the first HPF
The output signal of (6a) is supplied to the first fixed contact (7a) of the changeover switch (7), and the output signal of the second HPF (6b) is supplied to the second fixed contact (7b) of the changeover switch (7). The output signal of the first HPF (6a) and the output signal of the second HPF (6b) can be selected by switching the movable contact (7m) of the changeover switch (7). This movable contact (7m)
Is a central control unit (hereinafter referred to as CPU) (12)
Controls switching.

Then, a luminance signal obtained at the movable contact (7m) is supplied to a low-pass filter (hereinafter referred to as LPF) (9) via an amplifier (8). This LPF (9) is a filter that passes signals of 3 MHz or less.

Then, the luminance signal output from the LPF (9) is converted into a digital signal by an analog / digital converter (10) for converting an analog signal into a digital signal, and then supplied to an integrating circuit (11). Perform the integration process in step 11). In this case, the integration circuit (11) is a digital integration circuit that integrates the luminance levels of all focus detection points for one screen for each field. A plurality of focus detection points in one screen are set in advance near the center of the screen. Then, the integrated value data calculated by the integrating circuit (11) is supplied to the CPU (12).

Then, the CPU (12) supplies a predetermined drive signal to the motor (13) for rotating the focus ring (1a) based on the result determined from the integrated value data from the integration circuit (11) to perform focus adjustment. It is like that.

Next, the focus control operation performed by the CPU (12) will be described. When the focus control circuit is started, the CPU (12) switches the movable contact (7m) of the changeover switch (7) to the first fixed contact (7). 7a). By doing so, the baseband luminance signal extracted by the imaging signal processing circuit (4) from the imaging signal output by the CCD (2) is the first signal.
From the HPF (6a) to the LPF (9) via the changeover switch (7) and the amplifier (8). For this reason, the first HPF (6a) and the LPF (9) are 100 k
The signal components between Hz and 3 MHz are extracted.
After the luminance signal component is converted into a digital signal by the analog-to-digital converter (10), the data of all the focus detection points for one screen are integrated by the integration circuit (11). As an integrated value in this case, for example, the imaging object is at a distance of 2 m from the imaging surface of the video camera, and the distance to the focal point is
Assuming that the distance is 2 m, as shown in FIG. 2, a characteristic W of a curve whose integral value increases is obtained with the vertex when the focus ring (1a) of the imaging lens (1) is located at a distance of 2 m. Here, assuming that the rotation position of the focus ring (1a) is 1 m when the control circuit is activated, the CPU (1
Integrated value W ₁ is obtained in 2). At this time, the CPU (12) supplies a control signal to the motor (13) to
a) it is slightly rotated in both directions, or a CPU integrated value when rotates the focus ring (1a) in either direction from the integrated value W ₁ increases (12) is determined. When this determination operation is completed, the focus ring (1a) is rotated in a direction in which the integral value increases under the control of the CPU (12), that is, in a direction to increase the distance, and the maximum value W ₀ when the integral value is 2 m is obtained.
Is detected. In this case, since the focus ring (1a) detects the integral value W ₂ which is slightly reduced from the maximum value W ₀ a distance 2m once beyond the integral value W ₀ when the distance 2m is to be the maximum value CPU (12) discriminates and stops the focus ring (1a) at a position of 2m.

In this example, after detecting the maximum integral value W ₀ , the CPU (12) sets the movable contact (7) of the changeover switch (7).
m) is connected to the second fixed contact (7b). In this way, the baseband luminance signal extracted by the imaging signal processing circuit (4) is transmitted from the second HPF (6b) to the LPF (9) via the changeover switch (7) and the amplifier (8). Then, a signal component of 1 MHz or more and 3 MHz or less is extracted from the luminance signal, and the luminance signal component of 1 M to 3 MHz is converted into a digital signal by an analog / digital converter (10). ), The data of all the focus detection points for one screen are integrated.

Here, a description will be given of the luminance signal components of the band 1 MHz to 3 MHz. If only the high frequency components are extracted, the second
As shown by a characteristic H in FIG., A pulse of the signal only becomes slightly higher level H ₀ in focus near the 2m are obtained. Therefore, when the integrated value of the luminance signal of the band 1M~3MHz the CPU that it is level H ₀ (12) detects the focus adjustment are to be determined to be in focus. Actually, the CPU (12) detects whether or not a threshold value “a” which is substantially intermediate between the level H ₀ of the integrated value in the focused state and the level in the unfocused state is determined, and determines the focused state. .

In this case, in this example, the CPU (12) stores the integrated value data of the high-frequency component of 1 M to 3 MHz detected by the integration circuit (11) every field (1/60 second) for the immediately preceding 10 fields. The CPU (12) makes a focus determination based on the 10-field integrated value data. That is, when at least one time (one field) of the integrated value data for 10 fields exceeds the threshold value a, the CPU (12) determines that the camera is in focus. However, immediately after the movable contact (7m) of the changeover switch (7) is switched from the first fixed contact (7a) to the second fixed contact (7b), the integrated value data of the high-frequency component of 1M to 3MHz is As long as 10 consecutive fields are not obtained, focus determination is made only with the integrated value data of the stored fields.

Thereafter, while the integrated value of the luminance signal of the band 1 M to 3 MHz continues to detect the threshold value a or more in the data of 10 continuous fields, it is determined that the in-focus state is continued, and this 2 m
Maintain the focus position of. When it is no longer detected that the threshold value a is exceeded once in the integrated value for 10 fields, it is determined that the camera is out of focus, and the changeover switch (7) is again switched to the first fixed contact (7a). Connect 100k ~
A search is made for the top of the curve W with a wide band of 3 MHz.

It should be noted that the level of the characteristic H shown in FIG. 2 is not always constant, and has a certain correlation with the level of the integrated value b (see FIG. 2) at the focal point of a broadband luminance signal of 100 kHz to 3 MHz. Change with it. Therefore, if the CPU (12) changes the threshold value a according to the level of the integrated value b in a wide band, it is possible to perform a good focus determination.

As described above, according to the focus control circuit of the present embodiment, after the search for the focal point is once performed using the broadband luminance signal, the searched point (distance) is surely matched using the narrowband luminance signal of only the high frequency component. It can be determined whether or not it is the focus.
For this reason, it is not necessary to constantly rotate the focus ring with a small amount to determine the focal point as in the related art, and once in focus, the focus state is maintained without rotating the focus ring at all. It is possible to determine whether the object is out of focus due to movement of the subject or the like, and it is possible to quickly and accurately determine.

In this case, in this example, the in-focus point is determined based on the narrow-band luminance signal based on the integrated value data for 10 fields, so that even when the video camera is vibrating due to camera shake, etc. Focusing can be determined. That is, when the video camera is moving due to vibration due to camera shake or the like,
The video camera moves almost periodically. By analyzing the vibration state, it can be seen that the movement is a state where the camera is stationary and is moving almost periodically. Therefore, even if the integrated value of the luminance component of the second frequency band detected in the vibrated state is detected from the data of 10 fields corresponding to about 0.2 seconds as in this example, at least one field is detected. As the data, a value when the camera is substantially stationary is detected. If the value at this time is equal to or larger than the threshold a, it can be determined that the in-focus state is continued.

For this reason, even if the video camera is in a vibrating state, it is possible to determine the focus satisfactorily, and good autofocus control is performed even when a vibrating state such as camera shake occurs.

In the above-described embodiment, the in-focus determination is performed based on the detection data of 10 times (10 fields). However, the number of times is not limited to 10 times, and the focus determination is performed a plurality of times based on a period in which a good signal is detected. Should be fine. Further, although the band in which the focus determination is performed is set to the high frequency component of the luminance signal, the focus determination may be performed based on the luminance signal component of the narrow band in the low frequency band within the band 100 k to 3 MHz in which the focus is searched. good.

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

〔The invention's effect〕

According to the video camera of the present invention, by performing focus determination based on multiple times of detection data of a narrow-band luminance component,
Even when the camera is vibrating due to camera shake or the like, there is an advantage that a reliable focus determination is performed and a stable autofocus operation is performed even when the camera shakes.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a focus control circuit according to the present invention, FIG. 2 is a characteristic diagram for explaining the example of FIG. 1, and FIG.
FIG. 4, FIG. 4 and FIG. 5 are characteristic diagrams for explaining the conventional auto focus operation. (1) is an imaging lens, (1a) is a focus ring,
(4) is an imaging signal processing circuit, (6a) is a first high-pass filter, (6b) is a second high-pass filter, (7) is a changeover switch, (9) is a low-pass filter, and (12) is a central processing unit. , (13) are motors.

Claims (1)

(57) [Claims] An optical lens capable of adjusting a focus; an image pickup means for picking up image light incident through the optical lens; and a first band included in a luminance component of an image pickup signal output by the image pickup means. A first filter to extract, a second filter to extract a second band in the first band included in a luminance component of an image signal output by the imaging unit, and an output of the first filter. Switching means for selecting the output of the second filter; integration means for periodically integrating the filter output selected by the switching means for a predetermined period; and focusing determination based on the integration value of the integration means Do
And controlling the focus of the optical lens from the result of the determination and controlling the switching of the switching means. As the first band, as the optical system for obtaining the image signal becomes in focus, A band in which the integral value of the output of the first filter is gradually increased by the integrating means is selected. As the second band, only when the optical system for obtaining the image signal is substantially in focus, Selecting a band in which the integration value of the output of the second filter by the integration means is increased by a predetermined level, and determining the focus by the control means, integrating the output of the first filter by the integration means; After the focus of the optical lens is adjusted so that the integrated value becomes the highest, the output of the second filter is integrated by the integrating means, and the integrated value becomes higher by the predetermined level. When detecting one of the detected at least a predetermined time,
A video camera, which determines that the subject is in focus.