JPH01291580A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To reduce malfunction and to provide high sensitivity and accuracy by finding the size of a high frequency component included in a signal by quantizing a video signal and processing it by a digital filter, and driving and controlling the position of a lens so as to maximize the above value. CONSTITUTION:Incident image light from the lens 1 is converted to an electrical signal by an image pickup element 2, and is converted to the video signal by a signal processing circuit 3. Next, the video signal is quantized by an A/D converter 4, and is inputted to an arithmetic circuit 5, then, stored in a memory 51. The digital filter 52 is provided with a BPF characteristic, for example, of a band area of (500kHz to 2MHz), and passes only components of (500kHz to 2MHz) in the video signal. A detection circuit 53 detects the output of the digital filter 52, and outputs a signal proportional to the size of detected output. A control circuit 54 outputs a control signal to perform so-called (mountaineering control) to introduce the value of the output signal of the detection circuit 53 to maximize an evaluation function as the evaluation function to a motor driving circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Use of N'(i, Industry)] This invention relates to an automatic focusing device used in a video camera.

[Prior Art] FIG. 73 is a block circuit diagram of a conventional automatic focusing device disclosed in, for example, Japanese Patent Publication No. 39-5265 't'. In the figure, (1) is a lens, (21 is a lens (1)
) is an image sensor that converts the image formed by A 77 into an electric signal (A 77), (3) is an signal 5J/processing circuit that converts the output signal of the image sensor (2) into a video signal (11th degree beam), (7)
is the motor that drives the lens (1), (6) is the motor drive circuit, (8) is the differentiation circuit that differentiates the video signal -J, (
9) is an integrating circuit that also integrates the video signal, (lO
) is a control circuit that calculates (? lil output of (8)) = (output of integral circuit (9)), and uses this difference as an evaluation function to control the motor (7) so as to maximize the single value function. The lens (1) is driven to control the position of the lens (1).

Next, the operation will be explained. Lenses generally have low-pass characteristics with respect to spatial frequencies, and spatial frequency components finer than the resolution of the lens do not pass through the lens, and when the lens system is not focused, this spatial frequency It is known that the pass band for 200 nm exhibits even narrower low-pass characteristics.

The image light incident through the lens (1) is transmitted to the image sensor (2).
is converted into an electrical signal by a signal processing circuit (3
) is converted into a video signal (luminance signal). Corresponding to the low-pass characteristic of the lens (1) for spatial frequencies when the lens (1) is not in focus, this video signal is also band-limited and exhibits a low-pass characteristic; therefore, the video signal The size of high frequency components in the signal is determined by the lens (1)
The degree of focus is determined by the degree of focus, and the larger the high frequency component is, the closer to the in-focus state it is. Therefore, the magnitude of this high frequency component can be used as a focus evaluation function.

On the other hand, the level of the output of the differentiating circuit (8) changes depending on the high frequency components in the video signal, but the output of the integrating circuit (9) does not depend on the magnitude of the high frequency components in the video signal. Since the difference between (output of the differentiating circuit (8)) - (output of the integrating circuit (9)) is a value corresponding to the magnitude of the high frequency component in the video signal, as mentioned above, , this value is considered to be an evaluation function indicating the degree of focus.

The control circuit (lO) adjusts the order of the lens (1) so that the evaluation function is maximized and guides it to the in-focus point. This control operation will be described in detail. Now, consider a case where the motor (7) rotates and moves the lens (1) in one direction.

At this time, if the evaluation function increases as the lens (1) moves, the lens system is close to the in-focus point, so the control circuit (lO).

Lens (1) in the same direction as the motor drive circuit (6)
A control signal is output to rotate the motor (7) so as to drive the motor (7). Conversely, if the evaluation function decreases as the lens (1) moves, the lens system is moving away from the in-focus point, so the control circuit (lO) is controlled by the motor drive circuit (8).
A control signal is output to reverse the motor (7) so as to drive the lens (1) in the opposite direction. In this way, the control circuit (lO) controls the position of the lens (1) so that the evaluation function is maximized, and at the maximum point of the evaluation function, the lens (1) is at the in-focus position.

FIG. 4 is a block circuit diagram of another conventional automatic focusing device. In FIG. 0, the same reference numerals as in FIG. 4 indicate the same or corresponding parts.

(12) is a bandpass filter having a pass band of, for example, 500 KHz to 2 MKHz, and (13) is a detection circuit.

In this conventional example, the magnitude of the high frequency component contained in the video signal is detected by separating the high frequency component in the video signal with a band pass filter (12) and performing envelope detection on this with the detection circuit (13). The control circuit (11) uses the magnitude of the output of the detection circuit (13) as an evaluation function and controls the position of the lens (1) so that this evaluation function becomes maximum. Since this evaluation function indicates the degree of focus, the lens (1) is driven to the in-focus position by this control.

Furthermore, Fig. 5 is a block circuit diagram of a conventional automatic focusing device shown in Japanese Patent Publication No. 60-2827, which is an improved version of the conventional example shown in Fig. 4 and uses multiple bandpass filters. This realizes an automatic focusing device with higher performance.

In this conventional example, first to third bandpass filters (12a), (12b), (12c) having different passing frequency bands are used to separate high frequency components in a video signal.
and first to third detection circuits (13a), (13b) that perform envelope detection on the outputs of each bandpass filter, respectively.
, (13c), and the control circuit (14) controls the lens (1) from a state largely out of focus to one in-focus state.
To control the position of the lens (1), when the focus is far away from the focused point, the order of the lens (1) is controlled using the output of the bandpass filter with the lowest passing frequency band as an evaluation function, and the lens (1) is moved closer to the focused point. As time passes, the output of the bandpass filter with the highest pass frequency band is used as the evaluation function. Near the focal point, the output of the bandpass filter with the highest pass frequency band is used as the evaluation function, and this evaluation function reaches its maximum value. The lens (1) is configured to control the position of the lens (1) so as to

[Problems to be Solved by the Invention] Since the conventional automatic focusing device is configured as described above, the conventional device shown in FIG. Due to malfunction, sufficient performance cannot be achieved.

In addition, in the conventional device shown in Fig. 4, in order to obtain high focusing accuracy, the pass frequency band must be set high, but when the pass frequency band is set high, the focus deviates greatly from the in-focus point. In some cases, the control sensitivity decreases significantly.
It becomes difficult to achieve both high sensitivity and high accuracy.

Further, although the conventional device shown in FIG. 5 can solve the above-mentioned problems, it requires a plurality of expensive band-pass filters, so it is expensive.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain an inexpensive automatic focusing device that is less likely to malfunction, has high sensitivity, and high accuracy.

[Means for Solving the Problem] The automatic focusing device according to the invention of claim 1 quantizes a video signal using an A/D converter and processes the quantized signal with a digital filter, thereby converting the signal into a The device is equipped with an arithmetic circuit that determines the magnitude of the high frequency component contained in the image and drives and controls the position of the lens so that the high frequency component is maximized.

Further, the arithmetic circuit of the invention of claim 2 has a plurality of digital filters with different pass frequency bands, and when the focus is far from the in-focus point, the output signal of the digital filter with a low pass frequency band is used to perform the focusing. The lens position is driven and controlled using the output signal of the digital filter, which has a higher pass frequency band as it approaches the focal point.

[Function] The arithmetic circuit in the invention of claim 1 quantizes the video signal taken out from the image sensor with an A/D converter, extracts a specific frequency component with a digital filter, and calculates the magnitude of this output. The position of the lens is controlled to maximize this value.

Further, the arithmetic circuit of the second aspect of the present invention sequentially switches to a digital filter having a higher pass frequency band based on a change in the output level of the digital filter, and drives and controls the position of the lens using the output signal thereof.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
In the figure, the same reference numerals as in FIG. 3 indicate the same constituent parts, so the explanation will be omitted. (4) is an A/D converter that quantizes the output of the signal processing circuit (3); (5)
is an arithmetic circuit that performs calculations based on the digital output of the A/D converter (4) and outputs the result as a control output, and includes a memory (51) that stores the output of the A/D converter (4), and a memory ( a digital filter (52) that extracts a specific frequency component from the contents of the digital filter (51);
), and a control circuit (54) that determines a control signal output based on the output of the detection circuit (53).

Next, the operation of this embodiment will be explained. Lens (1
) is converted into an electrical signal by the image sensor (2), and converted into a video signal (111 degree signal 1) by the signal processing circuit (3).Then, this video signal is converted into an A/D converter. The signal is quantized by the unit (4), input to the arithmetic circuit (5), and stored in the memory (51). The digital filter (52) has a frequency of, for example, 500 KHz to
It has BPF characteristics with a band of 2 MHz, and only passes components of 500 KHz to 2 MHz in the video signal. The detection circuit (53) detects the output of the digital filter (52) and outputs a signal having a value proportional to the magnitude of the detected output. The control circuit (54) uses the value of the output signal of the detection circuit (53) as an evaluation function, and outputs a control signal to the motor drive circuit (8) to maximize this evaluation function, so-called "hill-climbing control." The hill climbing control operation of the control circuit (53) is similar to the operation of the conventional control circuit (11) shown in FIG.

In this way, like the conventional example, this embodiment operates so that the high frequency component contained in the video signal is maximized, and stops when the focal point is reached.

FIG. 2 is a diagram showing the configuration of the arithmetic circuit (5) according to another embodiment of the present invention, in which (52a), (52b), and (52c) are the frequencies of the passband of a specific center frequency, which are respectively Digital filter for extracting components (53a)
, (53b), (53c) are detection circuits that detect the magnitude of the output of each digital filter (52a), (52b), (52c), and (54) is a detection circuit (54).
This is a control circuit that determines a control signal based on the outputs of 3a), (53b), and (53c).

Next, the operation of this embodiment will be explained.

The output of the A/D converter (4) is stored in the memory (51). Digital filter (52a), (52b)
, (52c) are, for example, 100 to 500 each.
KHz.

500KHz ~ 1MHz, IMHz ~ 2MH
Since it is set to have a bandpass filter characteristic having a band of z, only a predetermined specific frequency component in the video signal is passed. Detection circuit (53a), (
53b) and (53c) output values corresponding to the magnitudes of the signal components in these passbands, respectively.

A band pass filter (5
2a), (52b), and (52c), it is known that the higher the passband, the larger the amount of change in the evaluation function with respect to the amount of focus shift near the in-focus point. It is necessary to set one pass band high.

On the other hand, in a bandpass filter with a high passband, the passing signal component, that is, the evaluation function, decreases rapidly as the focus point is shifted, and when the focus point is far off, the output of the evaluation function decreases significantly, resulting in a decrease in sensitivity. In order to do it,
It is not possible to perform control over a wide range from a nearby subject to a distant subject.

On the other hand, if the passband of the bandpass filter is low, the amount of change in the evaluation function with respect to the amount of defocus near the in-focus point is small, so it is not possible to improve the focusing accuracy. Since the evaluation function outputs to a certain extent even when the focus is significantly shifted, control can be performed over a wide range from nearby objects to distant objects. In addition, when the passband of the bandpass filter is low, depending on the response of the lens system, evaluation of the lens position other than the focused point may be performed during the state from a position where the focus is largely shifted from the focused point to the 1st focused point. Although there is a maximum value of the function, such a maximum value does not correspond to the maximum value of the evaluation function of a bandpass filter with a higher pass band frequency, and therefore can be distinguished from the true in-focus position.

The control circuit (54) of this embodiment utilizes the principle described above to control the output of the detection circuit (53a) of the digital filter (52a) with the lowest pass frequency band when the focus is largely out of focus. When the output level, which increases as the focus approaches the focus, exceeds the maximum value or a predetermined value, the output is switched to the output of the detection circuit (53b) of the digital filter (52b) with a high pass frequency band. The focusing operation is controlled, and a digital filter (52
Using the output of the detection circuit (53c) in c), control is performed to reach the final in-focus state. Such a control circuit (
54) "operation of r hill climbing control" is almost the same as the operation of the control circuit (14) in the conventional example shown in FIG.

In addition, in the above embodiment, an example was shown in which three sets each of the digital filter and the detection circuit were used, but it is also possible to use two sets, or four or more sets, and the same effect as in the above embodiment can be obtained. .

Furthermore, the arithmetic circuit (5) in the embodiment shown in FIGS. 1 and 2 can also be constructed using a microcomputer. In this case, the entire series of operations of the digital filter detection circuit and control circuit can be implemented in software (program processing) for the data stored in the memory, so that the apparatus can be constructed at a lower cost.

[Effects of the Invention] As described above, according to the present invention, since the A/D converted video signal is configured to extract signal components in a predetermined frequency band using a digital filter, it is possible to achieve high accuracy without malfunction due to noise. An automatic focusing device can be realized. Further, by using a digital filter, it is possible to construct a device with much less variation than in the past, and the device can be constructed at a lower cost.

Furthermore, by using multiple digital filters with different pass frequency bands, the output signal of the digital filter with a higher pass frequency band is selected in sequence according to the focus state, and control is performed based on this output signal, so that the focus can be greatly improved. This has the effect of providing an automatic focusing device that can control a wide range with sufficient sensitivity from a deviated state, and can bring the focus to a focused state with high accuracy near the focal point.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of one embodiment of this invention, FIG. 2 is a block circuit diagram of an arithmetic circuit of another embodiment of this invention,
FIG. 3 is a block circuit diagram showing the configuration of a conventional automatic focusing device, FIG. 4 is a block circuit diagram showing the configuration of another conventional automatic focusing device, and FIG. 5 is a block circuit diagram showing the configuration of another conventional automatic focusing device. FIG. 2 is a block circuit diagram showing the configuration of the device. (1)...Lens, (2)...Image sensor, (3)...
...Signal processing circuit, (4) ...A/D converter, (5)
... Arithmetic circuit, (6) ... Motor drive circuit, (7)
...Motor, (51) ...Memory, (52), (
52a), (52b), (52c)--Digital filter, (53), (53a), (53b)
, (53c)."detection circuit, (54)... control circuit. In each figure, the same reference numerals indicate the same or phase ratio parts.

Claims (2)

[Claims] (1) An image sensor that converts a subject image formed on an imaging surface into an electrical signal, a lens system that forms the subject image on the imaging surface, an A/D converter that quantizes the electrical signal, and and an arithmetic circuit that extracts a specific frequency component in the digital output of the A/D converter using a digital filter and drives the lens system to bring the lens system into focus so that the specific frequency component is maximized. Automatic focusing device. (2) It has multiple digital filters with different pass frequency bands, and when the focus of the lens system is far from the in-focus point, the lens system is driven by the output signal of the digital filter with a low pass frequency band, and the lens system 2. The automatic focusing device according to claim 1, further comprising an arithmetic circuit that drives the lens system by switching to an output signal of a digital filter having a higher pass frequency band as the focus approaches the in-focus point.