JPH08214202A - Focus controller for camera - Google Patents

Abstract

PURPOSE: To improve both of focusing speed and focusing precision. CONSTITUTION: Two luminance components having respectively different frequency bands are extracted from a video signal obtained by image pickup through two band pass filters 6, 7 and the integration values (a), (b) of respective luminance components are detected by respective integration circuits 8, 9. When both of a value a/b operated by an arithmetic circuit 10 and the value (a) are increased, a CPU 11 judges a current position as a non-focused position, and when the degree of increment of the value a/b is reduced or the degree has a tendency to decrease, judges the position is close to a focused position, increases the driving speed of a focus motor 12 on the non-focused position and reduces the driving speed in the vicinity of the focused position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera focus control device applied to a video camera or an electronic still camera having a solid-state image pickup device.

[0002]

2. Description of the Related Art Conventionally, an autofocus system (so-called hill-climbing servo system) that uses a video signal as a focus evaluation value has been adopted in a video camera or the like, but this system basically provides a focus evaluation value for each field. Since the focus motor is driven while being acquired and compared, there is a problem that the focusing time becomes long.

[0003]

Therefore, according to the present invention,
When the position of the focus lens is not near the in-focus position, the focus lens is driven at a high speed, and when it is near the in-focus position, it is driven at a low speed. It is an object of the present invention to improve the focusing speed without degrading the focusing accuracy.

[0004]

In order to achieve the above object, the present invention obtains a focus signal from a change of a luminance component in a video signal obtained by imaging, and performs focus control based on the focus signal. In a focus control device for a camera, which is performed, a means for detecting an increase / decrease in a ratio of luminance components in two arbitrary different frequency bands, a means for detecting an increase / decrease in a luminance component in one frequency band, and the detection results are obtained. And a means for changing the drive speed of the focus motor for driving the focus lens based on the determination result of the vicinity of the in-focus position and the out-of-focus position.

Further, the relationship between the threshold value for detecting the increase in the luminance component and the threshold value for detecting the maximum value after detecting the increase is changed between the in-focus position and the out-of-focus position. It is characterized in that it is provided with a means for.

Further, in the focus control device for the camera, means for detecting an increase / decrease in the ratio of luminance components in two arbitrary different frequency bands, means for detecting an increase / decrease in the luminance component in one frequency band, and the both detections Based on the result, the vicinity of the in-focus position and the out-of-focus position are determined, and when the out-of-focus position is determined, the drive speed of the focus motor that drives the focus lens is set to a predetermined speed and a predetermined cycle is set. When the detection result is obtained and the comparison calculation is performed, and it is determined that the focus position is close to, the drive speed of the focus motor is set lower than the predetermined speed, and the detection result is set in a cycle longer than the predetermined cycle. And means for performing comparison calculation.

Further, in synchronization with the cycle of the acquisition of the detection result and the comparison calculation, the drive speed of the focus motor is limited to a predetermined movement amount of the focus lens for each cycle.

Further, it is characterized in that the drive speed of the focus motor is gradually lowered immediately after the determination of the vicinity of the in-focus position is first made on the basis of the detection result and when the same determination is made thereafter. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing a schematic configuration of the first embodiment of the present invention. Reference numeral 1 is an image pickup lens system composed of a plurality of lens groups including a focus lens 2, and 3 is an image formed by the image pickup lens system 1. CC for photoelectric conversion of received subject image
Image pickup device 4 including D (charge coupled device) and the like, and image pickup device 3
The camera process unit 5 that outputs the output from the device as a video signal is a video signal processing circuit that performs various signal processing on the video signal and outputs the luminance signal separately. 6 and 7 are two bands having different cutoff frequencies. It is a pass filter (BPF), and the pass band of one BPF 6 is set to, for example, 100 kHz, and the pass band of the other BPF 7 is set to, for example, 500 kHz.

Further, 8 and 9 respectively integrate the luminance components of the two frequency bands output from the BPFs 6 and 7,
Two integrating circuits that output the evaluation value for focus, 10
Is an arithmetic circuit that receives the evaluation values from both integrator circuits 8 and 9 and performs various calculations to be described later. 11 is a microcomputer (CPU) that controls the operation of each component of the configuration. 12 is a focus motor that moves the focus lens 2. , 13 are focus motor control circuits for controlling the focus motor 12.

In the arithmetic circuit 10, one BPF 6
The current integrated value of the output from the other is the evaluation value a and the previous integrated value is the evaluation value a '. Similarly, the current integrated value of the output from the other BPF 7 is the evaluation value b, and the previous integrated value is the evaluation value b. ', Aa', a / b, a '/ b', a / b-a '/ b' are calculated and output to the CPU 11.

FIG. 3 shows the evaluation value a from one BPF 6.
Is an example of an evaluation value curve in which the position (extending amount) of the focus lens 2 is plotted as a parameter, and the evaluation value curve has a chevron shape as a whole. The apex of the evaluation value curve corresponds to the in-focus position, and the focus lens 2 gradually approaches the apex from the initial position due to the extension movement by the focus control based on the evaluation value. This is,
This is a so-called mountain climbing servo.

FIG. 4 shows an example of an evaluation value ratio curve in which the ratio (a / b) of the evaluation value a from one BPF 6 and the evaluation value b from the other BPF 7 is plotted with the position of the focus lens 2 as a parameter. Is.

As can be seen from FIGS. 3 and 4, both a and a / b increase from the out-of-focus position to the vicinity of the in-focus position, but the increase degree of a / b decreases near the in-focus position. , Or tends to decrease.

In the first embodiment, the above-mentioned evaluation value a,
The focus motor 12 shown in the flowchart of FIG. 1 is controlled based on a ', b, b'.

In FIG. 1, when the current evaluation value a is not the maximum value (NO in S1-1), the focus motor 12 is extended (S1-2), and the evaluation value a is judged. If there is (YES in S1-3), the focus motor 12 is driven so as to return the focus lens 2 to the lens position corresponding to the evaluation value a having the maximum value (S1-4).

In the step (S1-3), the evaluation value a
Is not the maximum value (NO in S1-3), focus lens 2
The evaluation values a, a ′, b, b ′ that change when
The relationship between the predetermined threshold values Δk (threshold value for evaluation value a) and Δk ′ (threshold value for evaluation value ratio a / b) is a> (a ′ + Δk) (S1 -5) and a / b> (a '/ b' + Δk ') (YES in S1-6), a and a / b exceed the thresholds Δk and Δk', respectively. Since it has increased, it is determined that the focus motor 12 is at the out-of-focus position, and the focus motor 12 is driven at high speed (speed V1) (S1-7) to shorten the arrival time from the out-of-focus position to the vicinity of the in-focus position. I am trying.

However, in the step (S1-6),
When a / b> (a '/ b' + Δk ') is not satisfied (NO in S1-6),
Although a is increasing, a / b is not increasing, so it is determined that the focus motor 12 is near the in-focus position and the focus motor 12 is rotated at a low speed.
By driving at (velocity V2, V2 <V1) (S1-8) and facilitating the focusing control in the vicinity of the focusing position, the focusing accuracy is improved.

In the step (S1-5), a> (a '
+ (Δk) (NO in S1-5) and a <(a'-Δ
If not k) (NO in S1-9), return to step (S1-2) so that the focus lens 2 is further extended (forward direction),
Also, not a> (a '+ Δk) (NO in S1-5) and a <
If it is (a'-Δk) (YES in S1-9), it is determined that the focus point is reached, the focus lens 2 is moved to that position in the opposite direction (S1-10), and then stopped. To do.

FIG. 5 is a flowchart relating to the control of the focus motor according to the second embodiment of the present invention. In the second embodiment, as described with reference to FIGS. 3 and 4, the focus motor is driven in a fixed direction. Then, the luminance component in the video signal obtained by imaging is integrated to obtain an evaluation value, which has the same configuration as the configuration described in FIG.

In FIG. 5, first, the maximum evaluation value Ymax
Is initialized (S2-1), and the focus lens 12 is extended (forward direction) by the focus motor 12 (S2-
2) The evaluation value Y1 is obtained in the same manner as described above (S2-3). When the evaluation value Y1 increases beyond the first threshold value Δk1 (NO in S2-4, S2-5), the increase status flag i
Is set (S2-6), the evaluation value Y1 and the focus lens position P1 at that time (the motor extension amount are also acceptable) are stored as maximum values Ymax and Pmax, respectively (S2-7), and
Returning to step (S2-2), the focus motor 12 is further driven in the forward direction to obtain the evaluation value Y1.

A second threshold value Δk2 that is greater than Ymax.
When a large value exceeding (Δk1> Δk2) is detected
(YES in S2-8), the value is set to Ymax, and Pmax is updated at the same time (S2-7). This process is repeated until the current value is smaller than the first acquired threshold value Δk1 and the evaluation value smaller than the evaluation value acquired immediately before is detected (S2-9). When this evaluation value is detected (YES in S2-9), the position of Pmax where Ymax is detected is regarded as the in-focus position, and the rotation direction of the focus motor 12 is set to the opposite direction, and Pmax is set. After returning the focus lens 2 to the position (S2-10 to S2-12), it is stopped.

Thereafter, the evaluation value monitoring mode is entered (S2
-13), if a change in the evaluation value is detected (YES in S2-14),
Returning to step (S2-2), the operation described above is performed, and
By setting k1 to an appropriate value, the effect of malfunction due to noise can be reduced, and by setting Δk2 to an appropriate value, the amount of overrun at the in-focus position is minimized. Therefore, the focusing speed can be improved.

By the way, in each of the above-described embodiments, the characteristic curve of the evaluation value relating to the luminance component may vary due to the subject, its condition, noise, etc. In that case, even in the vicinity of the in-focus position. However, the focus motor is driven at a high speed, the amount of overrun at the in-focus position increases, the captured image becomes unsightly, and the in-focus time may increase depending on the amount of overrun.

Therefore, in order to solve the above problem, the following control is performed in the third embodiment of the present invention. Also in this third embodiment, as described with reference to FIGS. 3 and 4, basically, the focus motor is driven in a fixed direction, and the luminance components in the image signal obtained by image pickup are integrated. The evaluation value is obtained and has the same configuration as that described in FIG.

FIG. 6 is a flowchart relating to the basic control of the focus motor based on the evaluation values a, a ', b, b'in the third embodiment, and when the current evaluation value a is not the maximum value (S3- (NO of 1), the focus motor 12 is extended (S3-2), the evaluation value a is determined, and if it is the maximum value (YES of S3-3), the evaluation value a exhibiting the maximum value is displayed.
The focus motor 12 is driven so as to return the focus lens 2 to the lens position corresponding to (S3-4).

In the step (S3-3), the evaluation value a
Is not the maximum value (NO in S3-3), focus lens 2
The evaluation values a, a ′, b, b ′ that change when
The relationship between a predetermined threshold value Δk (threshold value for evaluation value a) and Δk ′ (threshold value for evaluation value ratio a / b) is a> (a ′ + Δk) (S3 -5) and a / b> (a '/ b' + Δk ') (YES in S3-6), a and a / b exceed the thresholds Δk and Δk', respectively. Since it has increased, it is determined that the focus motor 12 is in the out-of-focus position, and the focus motor 12 is driven at high speed (speed V1) (S3-7) to shorten the arrival time from the out-of-focus position to the vicinity of the in-focus position. I am trying.

However, in the step (S3-6),
If a / b> (a '/ b' + Δk ') is not satisfied (NO in S3-6),
Although a is increasing, a / b is not increasing, so it is determined that the focus motor 12 is near the in-focus position and the focus motor 12 is rotated at a low speed.
By driving at (velocity V2, V2 <V1) (S3-8) and facilitating the focusing control in the vicinity of the focusing position, the focusing accuracy is improved.

In the step (S3-5), a> (a '
+ Δk) (NO in S3-5), and a <(a'-Δ
If it is not k) (NO in S3-9), return to step (S3-2) so that the focus lens 2 is further extended (forward direction),
Also, not a> (a '+ Δk) (NO in S3-5) and a <
In the case of (a'-Δk) (YES in S3-9), the focus lens 2 is moved in the opposite direction (S3-10), then extended and returned to step (S3-2).

FIG. 7 is a timing chart of the evaluation value acquisition / comparison operation and the focus motor drive in the third embodiment. When the focus motor 12 is driven at a high speed (hereinafter, referred to as a high speed drive mode). , CPU11
Then, the evaluation value is obtained and the comparison calculation is performed for each field, and as a result, if the value is decreased, the drive of the focus motor 12 is reversed.

In this case, the focus evaluation value to be compared is, for example, a value every 3 fields in consideration of the influence of flicker. That is, as shown in FIG. 7, the focus evaluation value (k + n + 3) in the (k + n + 3) field is compared with the data (k + n) three fields before. The drive of the focus motor 12 is controlled according to the comparison result. By doing so, when the focus motor 12 is driven at high speed, even if it is determined that the focus motor 12 is not near the in-focus position and is driven at high speed even though it is actually near the in-focus position,
It is possible to reduce the amount of overrun at the position where the focus evaluation value is maximum, reduce the uncomfortableness of the captured image until focusing, and shorten the focusing time.

On the other hand, when it is near the in-focus position, the focus evaluation value is acquired and calculated at intervals of, for example, three fields in consideration of the influence of flicker, and the focus motor is operated at a low speed.
Drive twelve. This makes it possible to minimize the amount of overrun of the in-focus position in the vicinity of the in-focus position, and to stop at the accurate in-focus position.

In the case of the high-speed drive mode as shown in FIG. 7, for example, even when 6-step driving is required, the VD (Vertica
In synchronism with the (lDrive) cycle, the focus motor 12 is driven with the amount of movement limited to two steps for each VD, so that evaluation values (for example, (k) and (k in FIG. 7) to be compared are compared.
+3), (k + n) and (k + n + 3), etc. can reduce the influence of the motor drive, so it is possible to compare with high accuracy and decrease from the peak value surely. And it can be detected quickly.

Further, in order to avoid the influence of noise, the means for reversing the focus motor 12 can surely decrease the focus evaluation value (that is, the direction away from the in-focus position) by detecting the decrease of the evaluation value twice in succession. It is effective in making a judgment. As described above, in the case of the third embodiment, since the decrease detection is performed while driving the focus motor 12, in the case of a normal (that is, good S / N ratio) subject,
Even with only one detection, there is sufficient reliability.

Therefore, in the high speed drive mode, for example, when a stepping motor is used as the focus motor 12, it is necessary to drive 6 steps instead of the vicinity of the in-focus position according to the comparison result of the evaluation values (actually, ,
Depending on the current focus lens position, the focus position may be overrun if 6 steps are driven),
If the first step is driven as three steps and the focus evaluation value obtained as a result decreases for the first time, the next step is driven as one step which is the minimum step, and the decrease determination is performed.

As described above, this is done by 6
Even if it is determined that the steps need to be driven, in some cases, 6 steps may not actually be required, and if the decrease is detected in the first 3 steps, the decrease is detected in the next 3 drive steps. This is because there is a high possibility that By doing so, it is possible to reliably detect a decrease in the evaluation value and reduce unnecessary overrun.

When a DC motor other than the stepping motor is used, the same effect can be obtained by controlling the driving speed instead of controlling the number of steps.

In each embodiment, the control signal output to the focus motor control circuit 13 is controlled by the CPU in the configuration of FIG.
11 and the arithmetic operation is performed by the arithmetic circuit 10. However, it is easy to configure the arithmetic operation by the software of the CPU 11. With this configuration, the arithmetic circuit 10 can be omitted.

[0040]

As described above, according to the focus control device for a camera of the present invention, according to the structure of claim 1, the ratio of the luminance components of two different frequency bands is increased or decreased and one of the luminance components is adjusted. By detecting the increase / decrease and controlling the drive speed of the focus motor in the vicinity of the in-focus position and the out-of-focus position according to the detection result (evaluation value), both the in-focus speed and the in-focus accuracy can be improved. .

According to the structure of claim 2, the threshold value for detecting the increase of the luminance component and the threshold value for detecting the maximum value after detecting the increase are made different from each other, whereby the non-focus position is detected. With this, it is possible to reduce erroneous determinations of increase or decrease of the evaluation value due to noise and the like, and to reduce the overrun amount at the in-focus position near the in-focus position, so that the in-focus speed can be improved.

According to the third aspect of the present invention, the focus lens is driven at a high speed at the non-focus position, while the focus lens is driven at a lower speed in the vicinity of the focus position than at the non-focus position. Moreover, the amount of overrun of the in-focus position can be suppressed and the accurate in-focus position can be obtained by performing the acquisition of the evaluation value that is the basis of the determination of out-of-focus / in-focus and the comparison calculation in a long cycle. The focus lens can be stopped.

According to the structure of claim 4, during the high speed driving, the focus lens is gradually moved by a predetermined amount to a required moving amount in synchronization with the cycle of the evaluation value acquisition and the comparison calculation. The influence of the drive of the focus motor on the evaluation value to be compared can be reduced, highly accurate comparison can be performed, and the in-focus position can be detected quickly and reliably.

According to the fifth aspect of the present invention, during the high speed driving, the required focus lens movement amount obtained from the result of the comparison calculation of the evaluation values is not immediately driven, and the first driving step is performed. When it is determined to be in the vicinity of the in-focus position by comparing the evaluation values based on the result of a small amount of movement drive with a predetermined amount of movement (when determining the in-focus position vicinity for two consecutive times)
By shifting to low speed driving with a smaller movement amount,
The focus position can be reliably detected, and the overrun of the focus position can be prevented.

[Brief description of drawings]

FIG. 1 is a flowchart relating to focus motor control in a first embodiment of a focus control device for a camera of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 3 is a relationship diagram between an evaluation value and a focus lens extension amount.

FIG. 4 is a relationship diagram between a ratio of evaluation values and a focus lens extension amount.

FIG. 5 is a flowchart relating to focus motor control in the second embodiment of the present invention.

FIG. 6 is a flowchart relating to focus motor control according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating acquisition of evaluation values according to the third embodiment of the present invention.
6 is a timing chart of comparison calculation and focus motor driving.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Imaging lens system, 2 ... Focus lens, 3 ... Imaging element, 4 ... Camera process part, 5 ... Video signal processing circuit, 6, 7 ... Band pass filter, 8, 9 ... Integration circuit, 10 ... Operation circuit, 11 ... CPU, 12 ... Focus motor, 13 ... Focus motor control circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication G03B 13/36

Claims (5)

[Claims] 1. A focus control device for a camera, which obtains a focus signal from a change of a luminance component in a video signal obtained by imaging and performs focus control based on the focus signal, in two arbitrary different frequency bands. Means for detecting an increase / decrease in the ratio of the luminance component of the, a means for detecting an increase / decrease in the luminance component of one frequency band, and a focus based on the determination result of the in-focus position vicinity and the out-of-focus position obtained by the both detection results A focus control device for a camera, comprising: means for changing a driving speed of a focus motor for driving a lens. 2. The relationship between the threshold value for detecting an increase in the luminance component and the threshold value for detecting the maximum value after detecting the increase is determined between the in-focus position and the out-of-focus position. The focus control device for a camera according to claim 1, further comprising a changing unit. 3. A focus control device for a camera, which obtains a focus signal from a change of a luminance component in a video signal obtained by imaging and performs focus control based on the focus signal, in two arbitrary different frequency bands. Means for detecting an increase / decrease in the ratio of the luminance component, a means for detecting an increase / decrease in the luminance component in one frequency band, and a judgment as to the vicinity of the in-focus position and the out-of-focus position based on the detection results of both When it is determined to be the in-focus position, the drive speed of the focus motor that drives the focus lens is set to a predetermined speed, and the detection result is acquired and comparison calculation is performed in a predetermined cycle, and it is determined to be near the in-focus position. In this case, the drive speed of the focus motor is set lower than the predetermined speed, and the detection result is acquired and the comparison calculation is performed in a cycle longer than the predetermined cycle. A focus control device for a camera, comprising: 4. The driving of the focus motor is limited to a predetermined focus lens movement amount in each cycle in synchronization with the cycle of the acquisition of the detection result and the comparison calculation. The focus control device for a camera according to item 3. 5. The driving speed of the focus motor is gradually reduced between immediately after the first determination of the vicinity of the in-focus position based on the detection result and when the same determination is made thereafter. The focus control device for a camera according to claim 3 or 4.