JPH087322B2 - Automatic focusing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device, and more particularly to an autofocus (autofocus) which performs automatic focus detection using a video signal (captured video signal) output from a video camera. Hereinafter, it will be referred to as an AF system).

[Prior Art] In recent years, as an AF method that makes full use of the characteristics of video cameras,
The so-called hill-climbing servo system, which detects the screen definition by the high frequency components in the video signal, drives the focusing lens to maximize the definition, and automatically adjusts the optical focus of the TV camera, Attention has been paid. Regarding this conventional hill climbing servo system (hereinafter referred to as hill climbing system), for example, NHK Technical Research 1965, 1st
Volume 7, No. 1, No. 86, pages 21 to 37 are described in detail, and FIG. 5 is a block diagram of the conventional automatic focusing device by the hill climbing method of FIG. 4, and FIG. 5 showing its operating characteristics. The contents will be briefly described with reference to FIG.

First, the light from the subject 1 incident through the focusing lens 2 forms an image on the photoelectric conversion means 3 and is output as an electric signal. An output signal as a video signal output from the photoelectric conversion means 3 is input to a process circuit 5 for a video camera via an amplifier 4, and at the same time, a band pass filter separately arranged in parallel after the amplifier 4 for AF detection. Only the high frequency component in the video signal is extracted by the (BPF) 6 and input to the gate circuit 7 in the next stage.

Further, from the horizontal synchronizing signal HD and the vertical synchronizing signal VD separated by the camera process circuit 5 described above, a window pulse forming circuit (WINDOW) 8 is used to preset a region of one screen, for example, only the central portion of the screen. , A so-called window pulse is formed, the window pulse is input to the gate circuit 7 described above, and the high frequency component signal is extracted and output only in the pulse generation section. The high frequency component signal output from the gate circuit 7 is further processed by a detector (DEF) 9 and an integrator 10.

The relationship between the voltage corresponding to the output of the integrator 10 (hereinafter referred to as the focal voltage) and the focal length of the lens 2 is shown in FIG. Since this focus voltage corresponds to the definition of the captured image, the position of the distance ring (focus ring) for moving and adjusting 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, at the just focus point (focus point position), the focus voltage becomes maximum,
As it deviates from this maximum position C, it decreases.

Therefore, as can be seen from FIG. 5, if some control means controls the position of the lens distance ring so as to climb the peak of the focus voltage and guides the lens distance ring to the top of the peak where the focus voltage becomes the maximum, Focusing will be possible. The control means is an integrator 10 for each field of the video signal.
It is known that the objective is achieved by holding the output of (1), comparing the value held last time and the value held this time for each field, and driving the lens distance ring in the direction in which it becomes larger. That is, as shown in a hill climbing circuit 16 surrounded by a broken line in FIG. 4, a mono-multivibrator (MM) 12 and a sample pulse forming circuit (SP) 13 are obtained from the vertical synchronizing signal VD separated by the camera process circuit 5 described above. By this, a sample pulse generated at a constant timing is formed, and the sample pulse holds the integrator output input to the sample hold circuit (S / H) 11 for each field. Further, the output of the sample and hold circuit 11 is branched into two, one of them is kept as it is, and the other is delayed by one field by a one field delay circuit (1 field Delay) 14 and input to a comparator 15 in sequence. The difference, that is, the difference between the integrator output of the previous hold and the integrator output of the current hold is calculated by the comparator 15.

If the focus voltage of the output of the integrator 10 is at the level A in the previous field and is at the level B in the next field, the focus voltages A and B are B> A, as shown in FIG.
Therefore, for example, a high-level control signal is output from the comparator 15 to the motor drive control circuit (DRIVER) 17, and the motor (Mo) 18 is driven while maintaining the direction as it is until now. By driving the motor 18, the lens 2 moves in the direction of the focal point. When the focus voltage is detected in the next field, assuming that the level of C in FIG. 5 is C> B, the signal level from the comparator 15 remains unchanged and the motor 18
Yes, they will move in the same direction.

At this time, as shown in FIG. 5, assuming that the maximum point of the focus voltage is at the level of C, if the lens distance ring is moved in the same direction by the motor 18 as a matter of course, the in-focus state of C is reversed. The focus voltage tends to decrease as the focus voltage decreases. As a result, the focus voltage of D level is output in the next field, and since D <C, the comparator 15 outputs a low level signal to the control circuit 17. With this low level signal, the control circuit 17 outputs a control signal for rotating the motor 18 in the reverse direction, and the lens distance ring is sent back in the focusing direction again.

As described above, in the conventional hill-climbing method shown in FIGS. 4 and 5, when the output of the hill-climbing circuit 16 configured by the comparator 15 and the like is positive (high level), that is, the focus voltage increases with time. If the output is from the hill climbing circuit 16, the output of the hill climbing circuit 16 is negative (low level), that is, if the focus voltage is decreasing with time, the motor 18 Reverse the direction of rotation and return to climbing the mountain. Therefore, by climbing a mountain as shown in FIG. 5 created by the focus voltage while referring to the output voltage of the integrating circuit 10, and finally oscillating in small steps at the top of the mountain, a steady state is reached. , Automatic focus detection will be performed.

As described above, in the hill climbing method, since the automatic focus detection is performed using the output signal itself from the image pickup means, it is not necessary to separately provide a component for automatic focus detection, and the focus detection can be performed relatively inexpensively and accurately. There is an advantage that you can.

[Problems to be Solved by the Invention] However, in the above-described conventional hill-climbing method, in order to determine whether or not the peak (maximum value) of the focus voltage in the focused state, it is necessary to get off the mountain once. However, since it cannot be determined whether or not it was the top of the mountain, there is a drawback that it reaches a steady state while vibrating in small steps near the top of the mountain. That is, in the focused state, the motor repeats forward and reverse rotations, climbs and descends near the top of the mountain, and is constantly vibrating in small steps. This vibration causes deterioration of the image quality and therefore needs to be removed.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks, to eliminate a state in which the lens vibrates in small steps at the peak of the focus point, and to provide an automatic focusing device which performs a correct focus operation.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an output means for sequentially outputting a signal corresponding to a focus degree in a predetermined cycle, and a plurality of output means output by the output means. Prediction means for predicting and calculating the in-focus point by substituting a signal into a predetermined function, and a level of the signal is equal to or higher than a first reference level, and two consecutive output signal levels output from the output means. When the difference is less than or equal to the second reference level, the control means performs focus adjustment based on the prediction result of the prediction means.

In one aspect of the present invention, the control means has a level of the signal lower than a first reference level, or a difference between two consecutive output signal levels output from the output means is a second level. When it is below the reference level, the focus adjustment is performed based on the difference between the two signals output from the output means without using the prediction result of the prediction means. You can

[Operation] According to the present invention, prediction is performed using a plurality of signals output by the output unit that sequentially outputs a signal corresponding to the focus degree at a predetermined cycle, and the prediction data is used only in the vicinity of the focus. Therefore, high prediction accuracy and reliability can be obtained, small vibrations at the focal point can be prevented, and high-speed focus adjustment can be performed.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

A. Basic Structure FIG. 1 shows the basic structure of the embodiment of the present invention. In the figure, a is an output unit that sequentially outputs signals corresponding to the focus degree at a predetermined cycle, and b is a prediction unit that predicts a focus using three or more signals output by the output unit a. Is. Reference numeral c is a control means, which performs focus adjustment based on the prediction result of the prediction means b when the level of the above-mentioned signal satisfies a predetermined condition.

B. Circuit Configuration FIG. 2 shows a circuit configuration of an embodiment of the present invention. In the figure, 19 is a 1-field delay circuit as an output means, which inputs the focus voltage B in the previous field delayed by 1 field by the 1-field delay circuit 14 in the previous stage and further delays it by 1 field before the previous field. The focus voltage A of is output. Numeral 20 is a peak predicting circuit as a predicting means, which uses the input focus voltage c of the current field, the focus voltage B of the previous field, and the focus voltage A of the field before two as a parameter with these A, B and C as parameters. Based on a known calculation formula, for example, a quadratic function prediction formula, it is predicted in what field the focus voltage P (see FIG. 3) at the top corresponding to the focused state will be predicted, and the predicted timing after N fields The signal is output as a gate signal, and the predicted top focus voltage P is output as a comparison signal.

As shown in FIG. 3, the focus voltage in the current field (i) is C, the focus voltage in the previous field (i-1) is B, and the focus voltage in the previous field (i-2) is A. Reference numeral 21 denotes a first subtraction circuit, which subtracts the focus voltage B from the above-mentioned focus voltage C and outputs a signal corresponding to CB. A second subtraction circuit 22 subtracts the focus voltage A from the focus voltage B described above and outputs a signal corresponding to BA.

Reference numeral 23 denotes a first comparator, which is a focus voltage C input to the non-inverting input terminal and a predetermined threshold V _{ref I} set at the inverting input terminal.
Is compared to determine whether C> V _{ref I} , and when a positive determination is made, a high level signal is output. Reference numeral 24 denotes a second comparator, which is an output (CB) of the first subtraction circuit 21 input to the inverting input terminal and a predetermined threshold V set at the non-inverting input terminal.
by comparing the _{ref II} determines whether C-B> V _{ref II,}
When the determination is affirmative, a high level signal is output. A third comparator 25 is an output (CB) of the first subtraction circuit 21 input to the inverting input terminal and an output (BA) of the second subtraction circuit 22 input to the non-inverting input terminal. Compare with and CB
<B-A is determined, and if a positive determination is made, a high-level signal is output.

An AND circuit (AND) 26 as a control means performs a logical product operation of the outputs of the three comparators 23, 24 and 25 described above, and opens the gate when all the outputs are at the high level, The signal of is output. The output signal of the AND circuit 26 is supplied as a control signal for the top prediction circuit 20 and a motor speed control signal. 27 is a fourth comparator, which is the predicted maximum focus voltage P from the peak prediction circuit 20 input to the non-inverting input terminal and the current focus voltage C in the current field from the sample hold circuit 11 input to the inverting input terminal. Is compared to determine whether P ≧ C, a positive determination is made, and a gate pulse (timing signal) from the top prediction circuit 20.
Outputs a motor stop signal when is ON. The comparator 27 itself may be configured to have a range of comparison judgment.

Reference numeral 28 denotes a motor control circuit (M / control) for driving and controlling the lens moving motor 18 for moving the distance ring of the focusing lens 2, which normally rotates the motor 18 when the output of the hill climbing circuit 16 is at a high level. , When the output is low level, the motor 18 is reversed. Further, the control circuit 28 makes the motor 18 low speed when the output of the AND circuit 26 is high level, makes the motor 18 high speed when the output is low level, and stops the motor 18 by the motor stop signal of the fourth comparator 27. The hill-climbing circuit 16 has substantially the same configuration as that of the conventional example shown in FIG. 4, operates according to the output of the first comparator, compares the focus voltages C and B, and when C> B, the motor It outputs a high level signal for normal rotation, and outputs a low level signal for motor reverse rotation when C <B.

Since the other components are the same as those of the conventional example shown in FIG. 4, detailed description thereof will be omitted.

C. Operation of Embodiment Next, the operation of the embodiment of the present invention shown in FIG. 2 will be described with reference to FIG.

The light of the subject 1 is imaged on the photoelectric conversion means 4 by the lens 2, and the video signal converted into an electric signal is the BPF 6, the gate circuit 7, the detector 9 and the integrator as in the conventional example described above with reference to FIG. Sample and hold circuit (S / H) 11 via device 10
Enter in and hold for each field. The output of the sample hold circuit 11 is the first field delay circuit 1 in the subsequent stage.
4, input to the first comparator 23, the first subtraction circuit 21, the fourth comparator 27, the top prediction circuit 20, and the hill climbing circuit 16, respectively.

The focus voltage B of the previous field delayed by one field by the first field delay circuit 14 is two subtraction circuits 21,2.
2 and the peak predicting circuit 20 and also to the second field delay circuit 19. The focus voltage A of the previous field, which is further delayed by one field by the second field delay circuit 19, is supplied to the second subtraction circuit 22 and the peak prediction circuit 20.

The subtraction output (CB) of the first subtraction circuit 21 is the second comparator 24.
Is supplied to the inverting input terminal of the third comparator 25, and the output of the second subtraction circuit 22 is supplied to the non-inverting input terminal of the third comparator 25. The current field focus voltage C output from the sample hold circuit 11 is compared with a predetermined threshold value V _{ref I} in the first comparator 23, and when C> V _{ref I}
A high level signal is output from 23 to the hill climbing circuit 16 and the AND circuit 26. The output (CB) of the first subtraction circuit 21 is compared with a predetermined threshold value V _{ref II} in the second comparator 24, and _CB
When <V _{ref II} , the comparator 24 outputs a high level signal to the AND circuit 26. Furthermore, the output (CB) of the first subtraction circuit 21 and the output (BA) of the second subtraction circuit 22 are the third
The comparator 25 compares them, and when CB <B-A, the comparator 25 outputs a high level signal to the AND circuit 26.

When all the judgment outputs of the above-mentioned comparators 23, 24 and 25 are at the high level, that is, when all the following conditional expressions that indicate that they are approaching sufficiently close to the maximum focus voltage P are satisfied, the AND circuit 26 It becomes a high level, and the top prediction circuit 20 is activated.

C> V _{ref I} C−B <V _{ref II} C−B <B−A In other words, as shown in FIG. 3, the focus voltage C of the current field is sufficiently high (C> V _{ref I} ) and the previous field is When the difference between the focus voltage B of the current field and the focus voltage B of the current field is less than a predetermined level (CB−V <V _{ref II} ), that is, when the slope of the peak is not so steep and is sufficiently close to the peak P, If the slope of the mountain determined in this field is smaller than the slope of the previous mountain (C-
B <B-A), when it is approaching the summit of the mountain and is sufficiently close to the summit of the mountain, the summation prediction circuit 26 is operated to set the focus voltage (estimated focus voltage) P at the summit of the summit. It is possible to easily predict how many more fields will elapse before the peak can be predicted by a simple quadratic function or the like.

In response to the output of the AND circuit 26 described above, the top prediction circuit 20 operates, and from the input focus voltages A, B and C, these
Based on a quadratic function with A, B, and C as parameters, the maximum peak focus voltage P corresponding to the focused state and the number of fields after which the maximum focus voltage P will be reached are predicted.

The peak predicting circuit 20 outputs the timing signal after N fields, which is predicted to reach the peak in N fields later, to the fourth comparator 27 as a gate signal and outputs the predicted maximum focus voltage P to the non-inverting input terminal of the comparator 27. Output to. The fourth comparator 27 opens the gate with the gate signal and outputs a motor stop control signal to the motor control circuit 28 under the condition of P ≧ C.

In the hill climbing circuit 16, the current field focus voltage C and the previous field focus voltage B are C> B as shown in FIG.
The motor 18 is rotated in the forward direction when
A control signal for reversing is output to the motor control circuit 28.
The motor control circuit 28 rotates the motor 18 in the forward direction or the reverse direction according to the output signal of the hill climbing circuit 16 and, if the output of the AND circuit 26 is at a low level, rotates the motor 18 at a high speed and outputs the output of the AND circuit 26. If is a high level, the rotation of the motor 18 is switched to a low speed rotation. Therefore, the motor control circuit 28 rotates the motor 18 at a high speed to bring it closer to the in-focus position when the top prediction circuit 20 is not operating, that is, when only the hill climbing circuit 16 is operating. The rotation is switched to stop the motor 18 according to the motor stop control signal output from the comparison circuit 27 when the 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 stopped accurately at the in-focus position.

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

[Effects of the Invention] As described above, according to the present invention, a signal corresponding to a focus degree is predicted using a plurality of signals output by an output unit that sequentially outputs the signal at a predetermined cycle, and Since the prediction data is used only in the vicinity of the in-focus point, high prediction accuracy and reliability can be obtained, small vibrations in the vicinity of the in-focus point can be prevented, and high-speed and accurate focus adjustment can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic structure 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 is a focal length for explaining the operation of the embodiment of the present invention. FIG. 4 is a characteristic diagram showing the relationship with the focus voltage, 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 ... Bandpass filter, 7 ... Gate circuit, 8 ... Wind pulse forming circuit, 9 ... Detector, 10 ... Integrator, 11 ... Sample and hold, 14, 19 ... … 1 field delay circuit, 16 …… Mountain climbing circuit, 20 …… Top prediction circuit, 21,22 …… Subtraction circuit, 23,24,25,27 …… Comparator, 26 …… And circuit, 28 …… Motor control circuit.

Claims (2)

[Claims] 1. An output means for sequentially outputting a signal corresponding to a focus degree at a predetermined cycle, and a prediction for predicting a focus by substituting a plurality of signals output by the output means into a predetermined function. The predicting means when the level of the signal is greater than or equal to a first reference level and the difference between two consecutive output signal levels output by the output means is less than or equal to a second reference level. And a control means for performing focus adjustment based on the prediction result of 1. 2. The control means has a first level of the signal.
Is less than the reference level, or the difference between two consecutive output levels output from the output means is less than the second reference level, the output result is output from the output means without using the prediction result of the prediction means. The automatic focusing device according to claim 1, wherein the automatic focusing device is configured to perform focus adjustment based on a difference between the two signals.