JPS63178672A - Imaging device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an imaging device.

[Conventional technology and its problems]

For example, conventional autofocus systems for cameras with imaging devices, such as video cameras, have either used an imaging signal from an image sensor to adjust the focus automatically, or used a dedicated sensor to detect the subject image and automatically adjust the focus. There are a so-called passive type that performs focus adjustment, and an active type that performs automatic focus adjustment by emitting infrared rays and calculating the subject distance from the reflected light, each of which has advantages and disadvantages.

In automatic focusing, if the movement of the lens lacks smoothness when out of focus, this is especially noticeable in pass-splash type cameras, which makes the monitor image look unnatural. In addition, in terms of video recording, all the steps up to the point where the lens comes into focus are recorded, which has the disadvantage of degrading the image quality during playback.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an imaging device that makes changes in a monitor image more natural when the image is out of focus.

[Means for solving problems]

The imaging device according to the present invention includes a detection means for detecting a focus adjustment state of a photographing optical system, an imaging means for converting an image formed by the optical system into an image signal, and a detection means based on a detection result of the detection means. and output means for limiting and outputting the passing frequency band of the imaging signal.

[Effect]

Since the output means forces the monitor image to have low sharpness during the out-of-focus stage, it is possible to prevent an unnatural monitor image from appearing during focus adjustment.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of the configuration of an embodiment of the present invention.

In FIG. 1, 10 is a photographing lens, 12 is an image sensor,
14 is a known video signal processing circuit that processes the output signal of the image sensor. 14a is a video output terminal of the illustrated video camera, which is connected to a known monitor device. The video signal processing circuit 14 includes a VCF (voltage control filter) 16 that functions as a low pass filter that removes the high frequency component of the luminance signal component of the video signal from the image sensor 12.

A VCF is a filter circuit whose cut-off frequency can be changed depending on its control voltage.

On the other hand, circuits 18-28 are for focus detection and automatic adjustment. Specifically, 18 is a high frequency component that extracts a high frequency component from the luminance signal component of the output signal of the image sensor 12.
A bus filter (HPF), 20 is a peak hold circuit that detects and holds the peak value of the output of the HPF 18 within one field screen, 22 is an A/D converter, and 24 is a focus detection described below. In addition to performing calculations for VCF
A microprocessor generates 16 control voltages. 26 is a motor drive circuit that drives the lens drive motor 28 in accordance with a control signal from the microprocessor 24. 30 is a D/A converter that converts the digital signal output from the microprocessor 24 into an analog signal voltage in order to adjust the cut-off frequency of the VCF 16.

A preamplifier and a matrix circuit that converts the image sensor output signal into a luminance signal, a color difference signal, etc. are connected to the output of the image sensor 12, but since they are not directly related to the present invention, illustration and explanation are omitted.

Next, the operation of the circuit shown in FIG. 1 will be explained. The luminance signal component of the output signal of the image sensor 12 is applied to the HPF 18, and its high frequency component is extracted.

The peak hold circuit 20 has HPF1 for each field.
8 is detected and applied to the A/D converter 22. A/D converter 22 converts it into a digital signal and sends it to microprocessor 24.

In general, automatic focusing methods that use the output signal of the image sensor compare the peak value of the high-frequency component of the previous field with the peak value of the high-frequency component of the current field, and adjust the focusing lens in the direction that increases the peak value. and stop the focusing lens when the peak values are equal or very similar between fields. That is, the output E of the peak hold circuit 20 increases as the lens drive progresses, as shown in FIG. 2 (1), and becomes a constant value after the lens stops. This method is usually called "hill climbing operation" based on the change curve of the peak value E, and the microprocessor 24 performs calculations for this purpose.

Mathematically, the microprocessor 24 determines that the in-focus state is reached when the differential of the peak value E becomes zero, and the motor 28
Stops driving. The differential waveform of the peak value E is shown in Figure 2 (2
). In the illustrated example, the motor 28 is stopped after t.

In the present invention, at the stage of adjusting the lens 10 position,
In order to make changes in the monitor image smooth, the image sensor 1
The high frequency component of the luminance signal component of the second output signal is canted, and all of the luminance signal component is reflected on the monitor image near the in-focus point. In order to do so, in the illustrated embodiment, the second derivative of the output E of the peak hold circuit 20 is calculated, and it is determined from its zero point that the vicinity of the in-focus point has been reached. The second-order differential curve of the peak value E is shown in FIG. 2 (3). That is, the microprocessor 24 determines that the focus is out of focus before the zero point (to) of the quadratic differential curve in FIG. 2 (3), and the D/A
The converter 30 is outputted with a digital signal corresponding to a control voltage that has a filter characteristic as indicated by the broken line 4o in FIG. A digital signal corresponding to a control voltage having characteristic 42 is output. Figure 2 (4) is D
3 shows a voltage waveform that the /A converter 30 applies to the VCF 16.

Of course, the control voltage that indicates the cut-off frequency of the VCF 16 may be changed by changing the polarity of the second-order differential value of the peak value E.

In addition, an integrator is used instead of the D/A converter 30, and the microprocessor 24 is kept at a high level from time t0 to time t when the lens 10 reaches the focused point, as shown in FIG. 2(5). The integrator outputs a voltage signal, and the integrator outputs a voltage signal.
A control voltage that gradually increases as shown in FIG. 2 (6) may be applied to the control input No. 6. In this way, the effect of focus adjustment appears more clearly on the monitor image.

Furthermore, after the time t1 when the lens 10 reaches the in-focus point, the control voltage to the VCF 16 is changed at an arbitrary rate of change,
The filter characteristic may be continuously changed from characteristic 40 to characteristic 42 in FIG. By doing so, changes in the image leading to the in-focus state can be freely controlled.

FIG. 4 shows a flowchart of the above operation of the microprocessor 24. The microprocessor 24 calculates the differential value and the second-order differential value of the peak value E by calculating E,%-
It has three variables of 2+ER-1+Ell, and a variable of its differential value ΔE7 and second-order differential value Δ''EH.

However, it is assumed that the current peak value is En in chronological order En-t+Ei-1+EnO. Rotate the motor 28 appropriately to obtain two peak values En-2* En-1
After obtaining, go to step S-1, read the current peak value E7, and calculate its differential ΔEn and second-order differential Δ2En
Calculate (S-2, 5-3). Second derivative Δ” Efi
If is positive (S-4), it is still far from the in-focus point, so VC
Lower the control voltage to F16 to lower the cut-off frequency L (S-5). On the other hand, if the second-order differential ΔtEfi is zero or negative (S-4), it is close to the in-focus point, so V
The control voltage to the CF 16 is increased to increase the cut-off frequency (S-6). Next, it is determined whether ΔE7 is substantially zero (S-7), and if it is substantially zero, it is determined that the in-focus point has been reached, and the motor 28 is stopped (S-8).

If it is not zero, check its polarity (S-9).

In the hill climbing method, the peak value E increases as it approaches the focused point, so if ΔE is negative (S-9), the focused point exists in the opposite direction, so the rotation direction of the motor 28 is reversed. (S-10). Then, the previous peak value En-+ is updated with the current peak value E7 (S-11
), return to the first step S-1 to read the peak value of the next field. On the other hand, ΔE. If is positive (S-9), the rotational direction of the motor 28 is appropriate, so substitute E7 for Efi-1 (S-12), and ΔE
Substitute ΔE7 for o−+ (S-13), Step S-1
Return to

After the motor 28 is stopped in step S-8, if the subject moves, for example, automatic focus adjustment must be performed again. As a restart method, for example, the peak value E7 at the in-focus stage (time point 11 in FIG. 2) is stored, and the stored peak value and the current peak value are successively compared to find a significant difference. If this occurs, the fourth
Just restart the routine shown in the figure.

As described above, in this embodiment, the second derivative ΔzB.

Since the control voltage of the VCF is controlled according to the amount of focus, it is possible to prevent an unsightly image from occurring when the image is out of focus. Furthermore, since the VCF is controlled so that the luminance signal passes through a sufficiently high frequency band during focusing, extremely high quality images can be obtained.

In the illustrated embodiment, ΔtE is used as a means for detecting the focus state.
Although A and ΔE7 have been calculated, it is clear that the present invention is not limited to this and that other methods and calculations may be used.

〔Effect of the invention〕

As can be easily understood from the above description, according to the present invention, the focus adjustment operation can be displayed visually and smoothly, and unnatural images can be prevented from appearing on the monitor screen during the focus adjustment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operating mode of the circuit in FIG. 1, and FIG.
A filter characteristic diagram of the CF 16, FIG. 4 is a diagram showing an operation flowchart of the microprocessor 24 of FIG. 1. 10--Lens 12-Imaging element 14-Video signal processing circuit 16-Voltage control filter 18--HPF
20...-Beak hold circuit 22...-A/D
Converter 24--Microprocessor 26--Motor drive circuit 28--Motor 30-D/A converter

Claims (2)

[Claims] (1) A detection means for detecting the focus adjustment state of the photographic optical system, an imaging means for converting the image formed by the optical system into an imaging signal, and a passing frequency of the imaging signal based on the detection result of the detection means. An imaging device comprising: an output means for outputting a limited band. (2) The apparatus according to claim 1, wherein the output means cuts off and outputs a high-frequency component of a luminance signal of the image pickup signal when out-of-focus is detected.