JPH01307374A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To make high sensitivity compatible with high accuracy by switching a pass band characteristic of a digital filter automatically by a signal generated from a control circuit. CONSTITUTION:A control circuit 54 sets the pass band of a digital filter 62 comparatively low if the focus is largely deviated from the focal point and the evaluation function of the system from the digital filter 52 reaching a detection circuit 53 in this state is used to control the automatic focus matching device and a control signal is generated so as to increase the pass band of the digital filter 52 gradually as the focusing is approached. As the focusing approaches the focal point, the pass band frequency of the digital filter 52 is increased and the device controls the system such that the final focusing is reached by using the evaluation function of the system reaching the detection circuit 53 from the digital filter 52 whose pass band frequency is highest near the focal point finally. Thus, high sensitivity and high accuracy are made compatible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focusing device suitable for automatically adjusting the focus to the optimum position in, for example, a video camera.

[Prior Art] Fig. 3 is a diagram showing the configuration of a conventional automatic focusing device disclosed in, for example, Japanese Patent Publication No. 39-5265. , (2) is an image sensor f-1 (3
) is a signal processing circuit that converts the signal of the image sensor (2) into a video signal (1!4 degree signal), (8) is a differentiation circuit that differentiates this video signal, and (9) is a signal processing circuit that also integrates the video signal. A control circuit that calculates the output of the differential circuit (8) - the output of the integral circuit (9), uses the difference as an evaluation function, and outputs a control signal so as to maximize the evaluation function. (6) is a motor drive circuit that drives the motor (7) in response to a control signal output from this control circuit (lO), and (7) is a motor that drives the lens (+).

Next, the operation of the configuration described in - will be explained.

Lenses are generally transparent to low spatial frequencies! It has a 4i S characteristic, and the sky open wave number component finer than the resolution of the lens does not pass through the lens, and the passband for spatial frequencies when the lens system is not in focus has an even narrower low-pass characteristic. It is known to show.

The light incident through the lens (+) is converted into an hypochondriacal signal by the image sensor (2), and then sent to the signal processing circuit (3).
is converted into a video signal by Corresponding to the narrow low-pass characteristic of the lens (+) with respect to spatial frequencies, if the lens system is not in focus, this video signal will also be band-limited and exhibit a low-pass characteristic. The magnitude of high frequency components in the signal is determined by the degree of focus of the lens system.
Since the larger the high frequency component is, the closer to the in-focus state it is, so the magnitude of this high frequency component can be expressed as the in-focus valence.

・On the other hand, the output level of the differentiating circuit (8) changes in size depending on the high frequency components in the video signal, or the output level of the differentiating circuit (9) depends on the magnitude of the high frequency components in the video signal. Therefore, the difference between the output of the differentiating circuit (8) and the output of the integrating circuit (9) is a value corresponding to the magnitude of the high 1.1,1 wave component in the video signal. , this difference value can be considered as an at valence number indicating the degree of focus.

The control circuit (10) adjusts the lens system so that the above-mentioned evaluation function is maximized to bring the device into focus, and this control operation will be described in detail.

Now, if the evaluation function is when the motor (7) is rotating and moving the lens (1) in one direction, or if it is increasing as the lens (1) moves, then the lens system is approaching focus. In this case, the lens (1) is connected in the same direction from the control circuit (■0) to the motor drive circuit (6).
Outputs 5) for control such as driving. Conversely, if the value function decreases as the lens (+') moves, it means that the lens system is moving away from focus. Circuit (6
) to drive the lens (1) in the opposite direction. A control signal is issued to completely reverse the motor (7).

In this way, the control circuit (1o) outputs a control signal so as to lead to the maximum at valence number. Then, the maximum point of the evaluation function is the in-focus state of the lens system.

FIG. 4 is a block diagram showing the configuration of another conventional example, where (12) is, for example, 5o.

A bandpass filter (hereinafter referred to as BPF) with a passband of 1 Hz to 2 MHz, (+:l) is a detection circuit, (!l) is a control circuit, and the other configurations are the same as in Fig. 3. Therefore, the same reference numerals are given and the description thereof will be omitted.

In the conventional example shown in FIG. 4, the high frequency components in the video signal are separated by B P
13) performs envelope detection to detect the magnitude of the high frequency component contained in the video signal, and the control circuit (11)
Alternatively, the lens (+) is driven so as to maximize this evaluation function using the magnitude of the output of the detection circuit (13) as an evaluation function. In this case as well, since the evaluation function indicates the degree of focus, automatic focus adjustment similar to that shown in FIG. 3 is performed by this control.

Furthermore, FIG. 5 is a block diagram showing the configuration of another conventional automatic focusing device disclosed in the Japanese Patent Publication No. 60-2 A27 YZ, which is the conventional example of FIG. 4 using one BPF. Improved multiple BPFs (12a), (121>
), (12c) and the corresponding detection circuits (1:l
By using a), (13b), and (1:tc), an 11 dynamic focusing device with higher performance is realized.

(14) in FIG. 5 is a control circuit, and the other configurations are the same as those in FIG. 314 and FIG.

In the conventional example shown in FIG. 5, three B P F (12a) are used to separate high frequency components in a video signal.

Using (+2b) and (+2C), each B P F
(12a), (12b).

Three detection circuits (13a), (13b), (1:lc) are used to detect the envelope of the output of (12c),
The three B P F (12a), (12b), (1
2c), for example, 100 to 500.
K11z, 500 old Iz~111111z,
It is set to 1-2M1lz. In the case of this conventional example, the control circuit (14) uses three B P F (1
2a), (12b), (12c) and the detection circuit (13a)
.

Among the combinations of (l: lb) and (l: lc), B P F (
The output of the system from 12a) to the detection circuit (1:la) is controlled as an evaluation function, and as the in-focus state approaches, the outputs of B P F (12b) and (12c), which have higher passbands, are determined by the Jf valence number. Finally, near the in-focus point, B P F (12
A C evaluation function is obtained from the output of the system from c) to the detection circuit (l:lc), and the lens (1) is driven so as to maximize this evaluation function. In this case as well, the evaluation function indicates the degree of focus, so this control can be used to
Automatic focusing similar to that shown in the figure is performed.

[A section that tries to invent or solve! &i] The conventional automatic focusing device is configured as shown below. For example, in the conventional example shown in FIG.
Due to malfunctions caused by noise in the branch circuit and detection circuit, sufficient performance could not be achieved.

In addition, in the conventional example shown in Fig. 4, the passband frequency must be set high to obtain high focusing accuracy, and if the passband frequency is set high in this way, the focus may deviate greatly from the focused point Since the control sensitivity of
It was difficult to achieve both high sensitivity and high accuracy.

Furthermore, in the conventional example shown in Fig. 5, although high sensitivity and highly accurate focusing performance can be obtained by using multiple BPFs, variations in the operating characteristics of the device occur due to variations in the passbands of the multiple BPFs. There are problems in that the device tends to be large and expensive, and the use of a plurality of PFs makes the entire device expensive.

This invention was made in order to solve the problems mentioned in L, and provides an automatic focusing device that has fewer malfunctions, can achieve both high sensitivity and high accuracy, and can be constructed at a low cost as a whole. The purpose is to

[Means for Solving the Problems] The automatic focusing device according to the present invention quantizes a video signal using an A/D converter, and processes the quantized signal with a digital filter to reduce the amount of information contained in the signal. The magnitude of the high frequency component is determined, and the driving of the lens system is controlled so that the magnitude of the high frequency component is maximized, and the passband characteristic of the digital filter L is determined depending on the degree of deviation from focus.
(It is characterized by being made to change.

[Operation] According to the present invention, an A/D converter and a digital filter are used to obtain the evaluation function, and after the A/D converter quantizes the video signal, the digital filter quantizes the video signal at a specific h';1 wave number. The control sensitivity is increased by extracting the acid content, determining the magnitude of the extracted frequency component, and controlling it to maximize it.Furthermore, by switching the passband characteristics of the digital filter using the signal generated by the control circuit. In addition to increasing control accuracy, it is also possible to improve control accuracy.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of an automatic focusing device according to an embodiment of the present invention, in which (1)
is a lens, (2) is an image sensor that receives the light passing through the lens (1) and converts it into an hypochondriacal signal, and (3) is an image sensor that receives the signal output from the image sensor (2) as a video signal. A signal processing circuit for converting, (4) an A/Df converter for quantizing the output of the signal processing circuit (3), and (5) an I-noted A/D converter (4) for quantizing the output of the signal processing circuit (3);
) is an arithmetic circuit that performs arithmetic operations based on the digital output of the arithmetic circuit (5) and outputs the result as a control circuit (6), which drives the motor (7) by the control signal output from the arithmetic circuit (5). A motor drive circuit (7) is a motor driven by the L motor drive circuit (6) and drives the lens (1).

21:8! l is a block diagram showing the detailed configuration of the L oil distribution calculation circuit (5), in which (51) is the above A
A memory that stores the output of the /D converter (4), (52) a digital filter that extracts frequency components in a specific passband determined by the control signal generated by the control circuit (54), and (53) the digital filter described above. (52) is a detection circuit that detects the magnitude of the output, (54) is the detection circuit (
A control circuit that determines a control signal based on the output of 53) is connected to the motor drive circuit (6) and is also connected to a digital filter (52) to determine the passband characteristics of the digital filter (52). Generates a control signal to control the

Next, the operation of the configuration described in section H will be explained.

Light incident from the lens (1) is converted into an electrical signal by the image sensor (2), and further converted into a video signal by the signal processing circuit (3). Next, this video signal is converted into LF by an A/D converter (4) and then input to an arithmetic processing circuit (5).

This arithmetic processing circuit (5) has a digital bunt pass filter that extracts a specific frequency 1\ component in the input:a f ratio signal, and calculates the magnitude of the output of this digital filter using the 1f value. As a function, the Fljl II signal is output to the motor drive circuit (6) to drive the motor (7) and adjust the lens (1) so that the evaluation function is maximized.

The operation of the arithmetic processing circuit (5) will be explained in detail based on FIG.

The output of the A/D converter (4) is stored in the memory (51). Now, the digital filter (52), for example 1
Assuming that the digital filter (52) is set to have bandpass filter characteristics with a band of 00 to 500Kllz, only certain frequency components in the video signal are passed. As a result, the detection circuit (53) outputs an image corresponding to the magnitude of the signal component in this passband.

It is known that the higher the passband of this bandpass filter, the greater the change in the evaluation function for the focus shift product near the in-focus point. High: 1; Needs to be fixed. On the other hand, in a bandpass filter with a high passband, the output of the evaluation function decreases rapidly as the first focal point is shifted, and when the first focal point is shifted significantly, the output of the evaluation function decreases significantly. It is only possible to control a 1"1 dynamic focusing device that targets a wide range from a subject at a certain position to a subject at a far position.

On the other hand, when the passband of the bandpass filter is low, the amount of change in the evaluation function relative to the focus shift near the focused point is small, so it is not possible to improve the focusing accuracy; Since the evaluation function has a certain level of output even in the state of a large blur, the device can be controlled over a wide range from nearby objects to distant objects. In addition, if the passband of the bandpass filter is low, depending on the response of the optical system, the evaluation function for the lens position may be changed in addition to the focused point during the transition from a position that is largely deviated from the focused point to the focused point. Is there a local maximum value? A local maximum value other than the focused point is an evaluation function of a bandpass filter with a higher pass band frequency, or it is not a local maximum value, so it should be distinguished from the true focus position. It's coming.

Using the above principle, the control circuit (54) of the automatic focusing device in this embodiment sets the pass band of the digital filter (52) relatively low in a state where the focus is largely out of focus. The automatic focusing device is controlled using the evaluation function of the system from the digital filter (52) to the detection circuit (53) in this state, and as the focus approaches, the digital filter (52)
A control signal is generated to gradually increase the height of the four bands. The digital filter (52
), the passband frequency becomes higher, and finally the passband frequency becomes the highest near the focused point.Using the evaluation function of the system from the digital filter (52) to the detection circuit (5 pieces), the final Control is performed to reach a focused state.

For example, assume that the passband frequency of the digital filter (52) is set to a bandpass filter characteristic having a band of 100 to 500 KHz, and consider a state in which the focus is largely deviated from the in-focus point, that is, a state in which the image is largely blurred. With the lens system normally used in video cameras, even if the focus is significantly out of focus, the video signal will have a 100 to 50
0, a signal corresponding to the (i) region of about H2 passes through to some extent, so in this case, the control circuit (54) performs the same operation as the control circuit (11) in the conventional example, and the evaluation function becomes larger. Through so-called hill-climbing control, the focus approaches 7.1. In this state, since the pass band of the pandobus filter is relatively low, there is little change in the evaluation function with respect to changes in focus of the lens system. Furthermore, depending on the response of the lens system, there may be a maximum value of the evaluation function other than the in-focus point on the way to in-focus. In the conventional example shown in No. 514, in order to avoid malfunctions caused by such a lens system, three bandpass filters are used, and when the evaluation function of the bandpass filter system with the lowest passband frequency takes a local maximum value. Then, the control circuit (
14) moves on to control using the evaluation function of a bandpass filter system with a high passband frequency as the evaluation function. In this embodiment, the same operation can be performed without using a plurality of band pass filters unlike the conventional example.

That is, by using a digital filter as the bandpass filter, the logic of the digital filter is set in advance so that the passband can be changed by n), and this passband is controlled by a control signal from the control circuit (54). In other words, the passband of the bandpass filter is 100 to 5
00 K117. When the lens (1) is adjusted to take the maximum value of the evaluation function under the condition that the focus of the lens system is largely deviated from the condition set in The digital filter (52) is controlled so as to reset the passband frequency of the filter (52) to be higher than the previous passband.

The digital filter (52) changes the passband frequency by the control signal of the control circuit (54), for example, 500.
Change from KIIz to IMIlz.

In the following state, the control circuit (54) is similar to the control circuit (11) in the conventional example, using the magnitude of the signal 1) corresponding to the band from 500 to 1M1ly as an evaluation function. The in-focus state is approached through so-called hill-climbing control in which the evaluation function becomes larger as the camera moves. Under this condition, the passband of the bandpass filter is slightly higher than in the initial state, so the change in the evaluation function with respect to a change in focus of the lens system is larger than in the initial state. The bandpass filter is set to such a band and the lens (1) is controlled to be adjusted.
If a new maximum value of the evaluation function exists, at that point the passband of the bandpass filter is cut to a higher frequency, for example, 1 to 2 MIIz, and similar control is performed using the evaluation function under this condition.

In order to switch the passband frequency of the control circuit (54) or the digital filter (52), a method is adopted in which the condition is that the evaluation function exceeds a predetermined constant value, rather than the maximum value of the evaluation function. You may. In this method, the passband of the digital filter (52) is first selected, for example, from 100 to 500 llz, and so-called hill-climbing control is performed to drive the lens (+) so that the evaluation function becomes large. This is as explained in the embodiment described in -L, or if the evaluation function exceeds a predetermined constant value before reaching its maximum value as the lens (1) moves, the control The passband frequency of the digital filter (52) is controlled by the control signal of the circuit (54), for example, from 500Hz to 1MI+7. Cut like a bell (
)Eru.

Furthermore, under this condition, if the 11f value function exceeds a constant A4, the passband will be cut to a higher passband J7i1 wavenumber, and finally a bandpass filter will be set in the highest passband. Similar control is performed using an evaluation function under the conditions.

The control circuit (54) determines the conditions in this way and sequentially
While changing the passband characteristics of the digital filter (52), the control output is outputted to the motor drive circuit (6) so as to perform so-called hill-climbing control that maximizes the evaluation function. The operation of the hill climbing control under each condition is almost the same as the operation of the control circuit (eye) in the conventional example.

In the manner described below, the imaging device operates so that the high frequency components contained in the video signal are maximized, and the imaging device comes into focus.

In addition, in the embodiment 1-1, an example was shown in which the passband frequency of the digital filter was divided into three setting conditions.
It may be possible to switch to any number of passband frequency setting conditions, as long as there are two or more.Furthermore, instead of cutting the passband frequency of the digital filter in stages, the control circuit ( 54) by the control signal of i! Even if it is changed continuously, the same functions and effects as in the above embodiment can be achieved.

Further, the arithmetic processing circuit (5) in the above embodiment can also be constructed using a microcomputer. In this case, the digital filter (52), the detection circuit (5 pieces) and the;
The entire series of operations of the control circuit (54) can be implemented in software and can be performed by one arithmetic processing circuit, which has the advantage that the device can be constructed at a lower cost.

[Effects of the Invention] As described above, according to this invention, bidet No. 4-1, which has been converted into a seed by A/Df:: conversion, is configured to be processed by a digital filter, and miscellaneous Hf. It is possible to realize a highly accurate automatic focusing device that does not malfunction due to , etc. Further, by using a digital filter, it is possible to construct a device with significantly less variation in performance compared to a conventional example constructed using a BPF, and the device can be constructed at a low cost.

Moreover, by controlling the passband characteristics of the digital filter, it is possible to control a wide range with sufficient sensitivity even when the focus is significantly out of focus, without using multiple bandpass filters, and to achieve high precision focusing near the focal point. It is possible to realize an automatic focusing device that achieves maximum focus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an automatic focusing device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of an arithmetic processing circuit constituting the automatic focusing device, and FIG. 3 is a block diagram showing the configuration of an automatic focusing device according to an embodiment of the present invention. Block l near I showing the configuration of the focusing device
, FIG. 4 is a block diagram showing the configuration of another conventional automatic focusing device, and 51X is a block IA showing the configuration of still another conventional automatic focusing device. (2)...Image sensor, (4)-A/D converter,
(5) Arithmetic processing circuit, (52) Digital filter, (54) Control circuit Note that the same reference numerals in the drawings indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 Figure 1: Shinsu 2: Kenweihe + Figure 3 Figure 42

Claims (1)

[Claims] (1) An image sensor that converts optical information of a subject image formed on an imaging surface into an electrical signal, an A/D converter that quantizes the electrical signal, and a digital output signal of this A/D converter. A digital filter that extracts a specific frequency component of the above, and an arithmetic circuit that includes a control circuit that outputs a control signal that maximizes the magnitude of the extracted specific frequency component to a driving circuit of the lens system. 1. An automatic focusing device, characterized in that the passband characteristic of the digital filter is automatically switched by a signal generated by the control circuit.