JPS62208013A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To eliminate minced vibrations of a lens in the vicinity of a focusing position by making a focus adjustment on the basis of the prediction result of a predicting means when the output difference between signals corresponding to the output extents of focusing is larger than a specific value. CONSTITUTION:An output means (a) outputs signals corresponding to the extents of focusing to the predicting means (b) at a specific period in order. The means (b) uses >=3 output signals from the means (a) to predict a focusing point. A control means (c) makes a focus adjustment on the basis of the prediction result of the means (b) when the output difference between two signals outputted by the means (a) is larger than the specific value, i.e. the difference between two signals outputted before said two signals are outputted. Consequently, the constitution is simplified and minced vibrations of the lens in the vicinity of the focusing point are eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic focusing device, and particularly to an automatic focusing device that performs automatic focus detection using a video signal (photographed video signal) output from a video camera. This is suitable for a device of the 8F type (hereinafter referred to as 8F).

[Conventional technology] In recent years, the ^F method, which takes advantage of the characteristics of video cameras, has been
The so-called rising servo method detects the definition of the screen based on the high-frequency components of the video signal, drives the focusing lens to maximize the definition, and automatically adjusts the optical focus of the TV camera. is attracting attention. This conventional mountain climbing method (hereinafter referred to as the mountain climbing method)
For example, see NHK Technical Research No. 17, 1965.
Although it is described in detail in Volume 1, Issue 86, Pages 21 to 37, Fig. 4 shows the configuration of a conventional mountain-climbing automatic focusing device, and Fig. 5 shows its operating characteristics. The contents will be briefly explained with reference to the characteristic diagram.

First, the light from the subject 1 that is incident through the focusing lens 2 forms an image on the photoelectric conversion means 3 and is output as an electrical signal. The output signal as a video signal from the photoelectric conversion means 3 is inputted to the process circuit 5 for the video camera via the amplifier 4, but at the same time, a bandpass filter is separately installed in parallel after the amplifier 4 for AF detection. (BPF) 8 extracts only high-frequency components from the video signal and inputs them to the gate circuit 7 at the next stage.

Further, from the horizontal synchronizing signal 110 and the vertical synchronizing signal VD separated by the above-mentioned camera process circuit 5, a window pulse forming circuit (WINDOW) 8 generates a preset area of one screen, for example, only the center of the screen. A synchronizing pulse, a so-called window pulse, is formed, and this window pulse is input to the above-mentioned gate circuit 7, and the above-mentioned high frequency component signal is extracted and output only during this pulse generation period. The high frequency component signal output from the gate circuit 7 is further processed by a detector (DEF) 9 and an integrator 10.

FIG. 5 shows the relationship between the voltage corresponding to the output of the integrator IO (hereinafter referred to as focal voltage) and the focal length of the lens 2. This focal voltage corresponds to the definition of the captured image, so the position of the distance ring (focusing ring) that moves and adjusts the position of the focusing lens 2 accurately matches the actual distance between the lens 2 and the subject 1. If it is, that is, just the focus point (focus point position), the focus voltage will be maximum,
As it deviates from this maximum position C, it decreases.

Therefore, as can be seen from Fig. 5, if the position of the lens distance ring is controlled by some control means so that it climbs the mountain of focal voltage, and the lens distance ring is guided to the top of the mountain where the focal voltage is maximum, it is possible to automatically This makes it possible to focus. This control means includes an integrator lO for each field of the video signal.
It is known that the objective is achieved by holding the output of , comparing the previously held value with the currently held value for each field, and driving the lens distance ring in the direction of increasing the value. That is, as shown in the mountain climbing circuit 16 surrounded by the broken line in FIG.
A mono multivibrator (MM) 12 and a sample pulse forming circuit (S, P
) 13 to form a sample pulse that is generated at a constant timing, and the integrator output input to the sample and hold circuit (S/H) 11 is sampled and held for each field using this sample pulse. Furthermore, the output of the sample-and-hold circuit 11 is branched into two parts, one of which is output as is, and the other is a 1-field delay circuit (1-field delay circuit).
y) 14, the signal is delayed by one field and input to the comparator 15 sequentially, and the difference between the two, that is, the difference between the integrator output of the previous hold and the integrator output of the current hold, is determined by the comparator 15.

Now, as shown in Fig. 5, if the focal voltage of the output of the integrator IO is at the level A in the previous field and at the level B in the next field, then the focal voltages A and B are BAA
Therefore, the comparator 15 outputs, for example, a high-level control signal to the motor drive control circuit (DRIVER) 17, and drives the motor (Mo) ta while maintaining the teno drive direction. By driving this motor 18, the lens 2 moves in the direction of the in-focus point. When the focal voltage is detected in the next field, assuming that it is at the level C in Fig. 5, C>B, so the signal level from the comparator 15 does not change, and the motor 18 always moves in the same direction. Become.

At this time, as shown in FIG. 5, the maximum point of the focal voltage is C
If the lens distance ring is moved in the same direction by the motor 18, it will naturally move away from the in-focus state of C, and the focal voltage will tend to decrease. As a result, in the next field, a D level focal voltage is output, and since D<C, the comparator 15 outputs a low level signal to the control circuit 17. In response to this low level signal, the control circuit 17 outputs a control signal for reversing the motor 18, and the lens distance ring is moved back toward the focusing direction again.

As described above, in the conventional mountain climbing method shown in FIGS.
When the output of the circuit 16 is positive (high level), that is, if the focal voltage is increasing over time, the rotation direction of the motor 18 is maintained as it is and the mountain climbing continues, and the output of the mountain climbing circuit 16 is negative (low level). At that time, that is, if the focal voltage is decreasing over time, the direction of rotation of the motor 18 is reversed to return it to the direction of climbing the mountain. Therefore, by climbing the mountain created by the focal voltage as shown in FIG. 5 while referring to the output voltage of the integrating circuit 10, and finally reaching a steady state at the top of the mountain while vibrating in small increments, , automatic focus detection will be performed.

In this way, in the hill-climbing method, automatic focus detection is performed using the output signal itself from the imaging means, so there is no need to separately provide components for automatic focus detection, and focus detection can be performed relatively inexpensively and accurately. It has the advantage of being able to

[Problems to be Solved by the Invention] However, in the conventional climbing method described above, in order to determine whether or not the peak of the focal voltage in the in-focus state is at the top (maximum value), it is necessary to climb down the peak once. For example, since it is not possible to determine whether or not the location is the top of a mountain, there is a drawback that a steady state is reached while vibrating in small increments near the top of the mountain. That is, in the focused state, the motor repeats forward and reverse rotation, climbs up and down near the top of the mountain, and is constantly vibrating in small increments. This vibration causes image quality deterioration and must be removed.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an automatic focusing device that performs focus adjustment by eliminating the state in which the lens vibrates in small increments at the top of the peak of the in-focus point.

[One Means for Solving the Problems] In order to achieve the present object, the present invention provides an output means for sequentially outputting signals corresponding to the degree of focus at a predetermined period, and three signals outputted by the output means. Prediction means for predicting the in-focus point using the above signals, and control for adjusting the focus based on the prediction result of the prediction means when the difference between the outputs of the two signals outputted by the output means is greater than or equal to a predetermined value. It is characterized by comprising means.

[Operation] In the present invention, the output means sequentially outputs signals corresponding to the degree of focus at a predetermined period, the prediction means predicts the focused point using three or more output signals, and the output means When the output difference between the two signals outputted by 5 is equal to or greater than a predetermined value, the control means performs focus adjustment based on the prediction result of the prediction means. Therefore, according to the present invention, the vibration of the lens of the imaging means near the focal point is eliminated, and the lens can be quickly stopped at the focal point.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

A. Basic configuration FIG. 1 shows the basic configuration of an embodiment of the present invention. In this figure, a is an output means that sequentially outputs signals corresponding to the degree of focus at a predetermined period, and b is a prediction means that predicts the in-focus point using three or more signals output by the output means a. It is. Control means C performs focus adjustment based on the prediction result of the prediction means A when the output difference between the two signals output by the output means a is equal to or greater than a predetermined value.

B0 Circuit Configuration FIG. 2 shows the circuit configuration of an embodiment of the present invention. In this figure, reference numeral 19 denotes a 1-field delay circuit as an output means, which inputs the focal voltage B in the previous field delayed by 1 field in the 1-field delay circuit 14 at the previous stage, and further delays the previous field by 1 field. outputs focal voltage A of . Reference numeral 20 denotes a top prediction circuit as a prediction means, which calculates a predetermined known calculation using A, B, and C as parameters from the input focus voltage C1 of the current field, the focus voltage B1 of the previous field, and the focus voltage A of the field before the previous field. For example, based on a prediction formula of a quadratic function, predict how many fields the top focal voltage P (see Figure 3) corresponding to the in-focus state will be, and then gate the timing signal after the predicted N fields. The predicted peak focal voltage P is output as a comparison signal.

Here, as shown in FIG. 3, it is assumed that the focal voltage in the current field (i) is C5, the focal voltage in the previous field (1-1) is B, and the focal voltage in the previous field (i-2) is A. A first subtraction circuit 21 subtracts the focal voltage B from the focal voltage C mentioned above and outputs a signal corresponding to C-8.

A second subtraction circuit 22 subtracts the focal voltage A from the aforementioned focal voltage B and outputs a signal corresponding to B-A.

24 is a first comparator, which compares the output (C-8) of the first subtraction circuit 21 inputted to its inverting input terminal with a predetermined threshold value Vrefl set to its non-inverting input terminal, and calculates that C-B <
It is determined whether or not V,=r+, and when the determination is affirmative, a high level signal is output. 25 is a second comparator, and the output (C-
8) The second subtraction circuit 2 inputs to the non-inverting input terminal.
It is determined whether C-B<B-8 by comparing the output (B-A) of No. 2 and outputs a high-level signal when the determination is affirmative.

2B is an AND circuit (AND) which performs an AND operation of the outputs of the two comparators 24 and 25, opens the gate when all the outputs are at high level, and outputs a high level signal. The output signal of the AND circuit 26 is supplied as a control signal to the summit prediction circuit 20. 27 is a third comparator, which compares the predicted maximum focus voltage P from the peak prediction circuit 20 inputted to the non-inverting input terminal with the current focus voltage C in the current field from the sample-hold circuit 11 inputted to the inversion input terminal. Compare and determine whether P≧C,
If the judgment is affirmative and the gate pulse from the summit prediction circuit 20 (
outputs a motor stop signal when the timing signal) is ON. The comparator 27 itself may be configured so that there is a certain degree of range in comparison/judgment.

28 is a motor control circuit (M/control) as a control means for driving and controlling the lens moving motor 18 for moving the distance ring of the focusing lens 2; The polarity (plus, minus) is determined, and when the polarity is positive, the motor 18 is rotated in the forward direction, and when the polarity is negative, the motor 18 is rotated in the reverse direction. Further, the motor control circuit 28 makes the motor 18 run at low speed when the level of the output (C-B) of the subtraction circuit is low, and makes the motor high speed when the level is high. In this way, the motor control circuit 28 switches the rotational direction of the motor 18 according to the polarity of the output of the subtraction circuit 21, and also variably controls the speed of the motor 18 according to the level of the output. . Furthermore, the motor control circuit 28 includes a third comparator 27
motor 18 in response to a motor stop signal supplied from
to stop.

The other components of the stage before the sample hold 11 are the same as those in the conventional example shown in FIG. 4, so detailed explanation thereof will be omitted.

Operation of the C1 Embodiment Next, referring to FIG. 3, the operation of the embodiment of the present invention shown in FIG. 2 will be described.

The light of the subject 1 is imaged by the lens 2 on the photoelectric conversion means 4, and the video signal converted into an electric signal is processed by a BPF 6, a gate circuit 7, a detector 9, and an integrator, as in the conventional example described above with reference to FIG. sample hold circuit (S/
H) 11 and held for each field. The output of the sample and hold circuit 11 is input to the first field delay circuit 14, first subtraction circuit 21, third comparator 27, and top prediction circuit 20 at the subsequent stage, respectively.

The focal voltage B of the previous field delayed by one field by the first field delay circuit 14 is transferred to the two subtraction circuits 21.
．． 22 and the summit prediction circuit 20, and the second
It is also supplied to the field delay circuit 19. The focal voltage A of the previous field, which has been further delayed by one field by the second field delay circuit 19, is supplied to the second subtraction circuit 22 and the top prediction circuit 20.

The subtraction output (C-B) of the first subtraction circuit 21 is output from the first comparator 2.
4 and the inverting input terminal of the second comparator 25, and the output of the second subtraction circuit 22 is supplied to the non-inverting input terminal of the second comparator 25. The output of the first subtraction circuit 21 (
C-B) is a predetermined threshold value Vrsf in the first comparator 24.
l, and when CB<Vrar+, the comparator 24
A high level signal is output from the AND circuit 26. Furthermore, the output (C-B) of the first subtraction circuit 21 and the output (B-A) of the second subtraction circuit 22 are compared in the second comparator 25, and when C-B<B-A, the comparator 25 outputs a high level signal to an AND circuit 26.

When the judgment outputs of the comparators 24 and 25 described above are all at a high level, that is, when the following conditional expressions indicating that the maximum focus voltage P is approaching sufficiently are satisfied, the AND circuit 26 is at a high level. Therefore, the summit prediction circuit 20 is activated.

C-B <Vrer+ C-B<B-A In other words, as shown in FIG. ), that is, when the slope of the mountain is not so steep and is sufficiently close to the summit P, and the slope of the mountain judged in this field is smaller than the slope of the mountain last time. (C
-B<B-A), since it is approaching the top of the mountain and is sufficiently close to the top of the mountain, the summit prediction circuit 26 is activated to calculate the focal voltage (predicted focal voltage) P at the top of the mountain. Using a simple quadratic function or the like, it is easy to predict how many fields it will take to reach the top.

The top prediction circuit 20 responds to the output of the AND circuit 26 described above.
is activated, and from the human-powered focal voltages A, B, and C, based on a quadratic function with these A, B, and C as parameters,
The maximum focal voltage P at the peak corresponding to the in-focus state and the number of remaining fields in which the maximum focal voltage P will be reached are predicted, and these predicted values are corrected using lens information supplied from the control circuit 30. For example, when the zoom lens is moving, the focal length etc. change moment by moment, so the previous predicted value P after several fields may not match and may go up or down, so this predicted value is based on the lens information. The peak prediction circuit 20 performs the correction.

The peak prediction circuit 20 outputs the timing signal after N fields predicted to reach the peak in N fields to the third comparator 27 as a gate signal, and also outputs the predicted maximum focal voltage P to the non-inverting input terminal of the comparator 27. Output to. The third comparator 27 opens its gate with the gate signal, and P
A motor stop control signal is output to the motor control circuit 28 under the condition of 2O.

The motor control circuit 28 has a positive polarity depending on the polarity of the output of the subtraction circuit 21, that is, the current field focal voltage C and the previous field focal voltage B are such that C>B as shown in FIG. When the polarity is negative, that is, C<B, the motor 18 is rotated in the reverse direction. Further, the motor control circuit 28 rotates the motor 18 in the forward or reverse direction, and also rotates the motor 18 at high speed if the level of the output (C-B) of the subtraction circuit 21 is equal to or higher than a predetermined level. Output (C-B)
If the level is below a predetermined level, the rotation of the motor 18 is switched to low speed rotation. Therefore, the motor control circuit 28 rotates the motor 18 at high speed when it is far from the in-focus position to bring it closer to the in-focus position, and when it approaches the in-focus state, the motor 18
The motor 18 is switched to low speed rotation, and the motor 18 is stopped in response to a motor stop control signal output from the comparator circuit 27 when the in-focus position is reached. Therefore, according to this embodiment, the lens 2 does not vibrate near the in-focus position, and the lens 2 can be quickly stopped at the in-focus position.

Note that the present invention is not limited to outputting a signal corresponding to the degree of focus from the output of the imaging means as in the present embodiment, and for example, a line sensor that indicates the degree of focus may be provided separately from the image pickup means. It is also applicable when using

[Effects of the Invention] As explained above, according to the present invention, the in-focus point is determined using three or more signals output from the output means that sequentially outputs signals corresponding to the in-focus degree at a predetermined period. When the difference between the outputs of the two predicted signals output from the output means is equal to or greater than a predetermined value, focus adjustment is performed based on the result of the above prediction, so the configuration is simple and the in-focus point is adjusted. This has the effect of eliminating small vibrations near the location (the top of the mountain).

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of the embodiment of the present invention, Fig. 2 is a circuit diagram showing the circuit structure of the embodiment of the present invention, and Fig. 3 shows the focal length and FIG. 4 is a block diagram showing the circuit configuration of the conventional example, and FIG. 5 is a characteristic diagram showing the operation of the conventional example. 3... Photoelectric conversion means, 6... Band pass filter, 7... Gate circuit, 8... Window pulse forming circuit, 9... Detector, 10... Integrator, II... Sample hold, 14.19...1 field delay circuit, 20...Top prediction circuit, 21.22...Subtraction circuit, 24.25.27...Comparator, 26...AND circuit, 28 ...Motor control circuit. t゛＋■ Figure 3 showing the answer to the example

Claims (1)

[Claims] 1) a) Output means for sequentially outputting signals corresponding to the degree of focus at a predetermined period, and b) A point of focus is determined using three or more signals outputted by the output means. and c) control means for adjusting focus based on the prediction result of the prediction means when the difference between the outputs of the two signals output by the output means is equal to or greater than a predetermined value. An automatic focusing device characterized by: 2) The automatic focusing device according to claim 1, wherein the predetermined value is a value based on a difference between two signals output before the two signals are output. .