JP3586003B2 - Focus control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a focus control device applied to a video camera or an electronic still camera equipped with a solid-state imaging device.
[0002]
[Prior art]
Conventionally, an auto-focus method (so-called hill-climbing servo method) using a video signal as a focus evaluation value has been adopted in a video camera or the like, but this method basically obtains a focus evaluation value for each field and compares the focus evaluation values. However, since the focus motor is driven, there is a problem that the focusing time becomes long.
[0003]
[Problems to be solved by the invention]
Therefore, in the present invention, when the position of the focus lens is not near the focus position, the focus lens is driven at a high speed, and when the focus lens is near the focus position, the focus lens is driven at a low speed. An object of the present invention is to achieve an improvement in focusing speed, which has been a problem in focus control, without deteriorating focusing accuracy.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a focus control device that obtains a focus signal from a change in a luminance component in a video signal obtained by imaging and performs focus control based on the focus signal. Means for detecting an increase or decrease in the ratio of the luminance components of the two frequency bands, means for detecting an increase or decrease in the luminance component of one of the frequency bands, and luminance of any two different frequency bands based on the detection results of the two means. When the ratio of components does not increase and only the luminance component in one frequency band increases, it is determined that the focus position is near the focus position, otherwise, it is determined that the focus position is out of focus. Means, when the in-focus position determining means determines that the focus position is out of focus, sets the drive speed of the focus motor that drives the focus lens to a predetermined speed, and sets the drive speed to a predetermined cycle. The acquisition of the detection result and the comparison operation are performed, and when it is determined that the focus position is near the focus position, the driving speed of the focus motor is set to be lower than the predetermined speed, and the detection result is obtained at a period longer than the predetermined period. Means for performing acquisition and comparison operation.
[0005]
Means for changing the relationship between a threshold value for detecting an increase in the luminance component and a threshold value for detecting a maximum value after detecting the increase between the vicinity of the in-focus position and the out-of-focus position It is characterized by having.
[0006]
In addition, in synchronization with the cycle of the acquisition of the detection result and the comparison operation, the drive speed of the focus motor is limited to a predetermined focus lens movement amount and driven in each cycle.
[0007]
Further, the drive 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 determination is made thereafter.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.
[0009]
FIG. 2 is a block diagram showing a schematic configuration of the first embodiment of the present invention. Reference numeral 1 denotes an imaging lens system including a plurality of lens groups including a focus lens 2, and reference numeral 3 denotes a subject imaged by the imaging lens system 1. An image sensor, such as a CCD (Charge Coupled Device), which receives an image and performs photoelectric conversion, 4 is a camera process unit that outputs an output from the image sensor 3 as a video signal, and 5 performs various signal processing on the video signal. Or a video signal processing circuit that separates and outputs a luminance signal, and 6 and 7 are two band-pass filters (BPFs) having different cutoff frequencies. The pass band of one BPF 6 is set to, for example, 100 kHz, and the other BPF 7 The pass band is set to, for example, 500 kHz.
[0010]
Further, 8 and 9 are two integrating circuits for respectively integrating the luminance components of the two frequency bands output from each of the BPFs 6 and 7 and outputting an evaluation value for focusing. An arithmetic circuit that receives the evaluation value and performs various calculations described later, 11 is a microcomputer (CPU) that controls the operation of each component, 12 is a focus motor that moves the focus lens 2, and 13 is a focus that controls the focus motor 12. It is a motor control circuit.
[0011]
In the arithmetic circuit 10, the current integrated value of the output from one BPF 6 is set as an evaluation value a, the previous integrated value is set as an evaluation value a ', and similarly, the current integrated value of the output from the other BPF 7 is set as an evaluation value b If the previous integrated value is the evaluation value b ', a-a', a / b, a '/ b', and a / ba-'/ b' are calculated and output to the CPU 11.
[0012]
FIG. 3 is an example of an evaluation value curve in which the evaluation value a from one BPF 6 is plotted using the position (extending amount) of the focus lens 2 as a parameter, and the evaluation value curve has a mountain 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 by the extension movement by the focus control based on the evaluation value. This is a so-called hill-climbing servo.
[0013]
FIG. 4 is an example of an evaluation value ratio curve in which the ratio (a / b) between the evaluation value a from one BPF 6 and the evaluation value b from the other BPF 7 is plotted using the position of the focus lens 2 as a parameter.
[0014]
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 a / b increases or decreases near the in-focus position. Tend to.
[0015]
In the first embodiment, the control of the focus motor 12 shown in the flowchart of FIG. 1 is performed based on the evaluation values a, a ', b, and b' described above.
[0016]
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 determined. (YES in S1-3), the focus motor 12 is driven to return the focus lens 2 to the lens position corresponding to the evaluation value a exhibiting the maximum value (S1-4).
[0017]
In the step (S1-3), if the evaluation value a is not the maximum value (NO in S1-3), the evaluation values a, a ', b, and b' that change when the focus lens 2 is extended are predetermined. The relationship between the threshold value Δk (threshold value for the evaluation value a) and Δk ′ (threshold value for the evaluation value ratio a / b) is a> (a ′ + Δk) (S1-5 If (YES) and a / b> (a '/ b' + Δk ') (YES in S1-6), a and a / b increase beyond the thresholds Δk and Δk', respectively. The focus motor 12 is determined to be at the out-of-focus position, and the focus motor 12 is driven at a high speed (speed V1) (S1-7) so as to shorten the arrival time from the out-of-focus position to the vicinity of the in-focus position. I have.
[0018]
However, if it is not a / b> (a '/ b' +. DELTA.k ') in step (S1-6) (NO in S1-6), a increases but a / b does not increase. Therefore, it is determined that the focus is near the focus position, and the focus motor 12 is driven at a low speed (speed V2, V2 <V1) (S1-8), thereby facilitating the focus control near the focus position. The focus accuracy is improved.
[0019]
In step (S1-5), if a> (a '+. DELTA.k) is not satisfied (NO in S1-5) and a <(a'-. DELTA.k) is not satisfied (NO in S1-9), focus lens 2 Return to the step (S1-2) so as to further advance (forward direction), and if a> (a '+. DELTA.k) but not (NO in S1-5) and a <(a'-. DELTA.k) ( In S1-9, YES), the focus lens 2 is determined to be the focal point, the focus lens 2 is moved in the reverse direction to that position (S1-10), and then stopped.
[0020]
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. The evaluation value is obtained by integrating the luminance components in the video signal obtained as described above, and has a configuration similar to the configuration described with reference to FIG.
[0021]
In FIG. 5, first, the maximum value Ymax of the evaluation value is initialized (S2-1), and the focus lens 2 is extended (forward direction) by the focus motor 12 (S2-2). An evaluation value Y1 is obtained (S2-3). If the evaluation value Y1 has increased beyond the first threshold value Δk1 (NO in S2-4, S2-5), an increase status flag i is set (S2-6), and the evaluation at that time is performed. The value Y1 and the focus lens position P1 (the motor extension amount is also possible) are stored as the maximum values Ymax and Pmax, respectively (S2-7), and the process returns to step (S2-2), and further the focus motor 12 is moved in the forward direction. By driving, an evaluation value Y1 is obtained.
[0022]
If a value larger than the second threshold value Δk2 (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 processing is repeated until an evaluation value whose current value is lower than the first threshold value Δk1 and smaller than the evaluation value obtained immediately before is detected (S2-9). When this evaluation value is detected (YES in S2-9), the position of Pmax at which Ymax is detected is regarded as the focus position, and the rotation direction of the focus motor 12 is set to be in the opposite direction. After returning the focus lens 2 to the position (S2-10 to S2-12), the focus lens 2 is stopped.
[0023]
Thereafter, the monitor enters the evaluation value monitoring mode (S2-13). If a change in the evaluation value is detected (YES in S2-14), the process returns to step (S2-2) to perform the above-described operation, and the Δk1 Can be set to an appropriate value to reduce the effect of malfunction due to noise, and by setting Δk2 to an appropriate value, the amount of overrun at the in-focus position can be minimized. Therefore, the focusing speed can be improved.
[0024]
By the way, in each of the above-described embodiments, the characteristic curve of the evaluation value related to the luminance component may vary depending on the subject, the condition thereof, noise, and the like. Is driven at a high speed, the overrun amount of the focus position increases, and the captured image becomes difficult to see, and the focusing time may be prolonged according to the overrun amount.
[0025]
Therefore, in order to solve the above problem, the following control is performed in the third embodiment of the present invention. Also in the third embodiment, as described with reference to FIGS. 3 and 4, basically, the focus motor is driven in a fixed direction, and the luminance component in the video signal obtained by imaging is integrated. An evaluation value is obtained, and has the same configuration as the configuration described in FIG.
[0026]
FIG. 6 is a flowchart relating to the basic control of the focus motor based on the evaluation values a, a ', b, and b' in the third embodiment. When the current evaluation value a is not the maximum value (NO in S3-1). ), The focus motor 12 is extended (S3-2), and the evaluation value a is determined. If it is the maximum value (YES in S3-3), the lens position corresponding to the evaluation value a exhibiting the maximum value is determined. Then, the focus motor 12 is driven so that the focus lens 2 is returned (S3-4).
[0027]
In the step (S3-3), if the evaluation value a is not the maximum value (NO in S3-3), the evaluation values a, a ', b, and b' that change when the focus lens 2 is extended are predetermined. The relationship between the threshold values Δk (the threshold value for the evaluation value a) and Δk ′ (the threshold value for the evaluation value ratio a / b) is a> (a ′ + Δk) and (S3-5 If (YES) and a / b> (a '/ b' + Δk ') (YES in S3-6), a and a / b increase beyond the thresholds Δk and Δk', respectively. Therefore, the focus motor 12 is determined to be at the out-of-focus position, and the focus motor 12 is driven at a high speed (speed V1) (S3-7), so as to shorten the arrival time from the out-of-focus position to the vicinity of the in-focus position. I have.
[0028]
However, if it is not a / b> (a '/ b' +. DELTA.k ') in step (S3-6) (NO in S3-6), a increases but a / b does not increase. Therefore, the focus motor 12 is determined to be in the vicinity of the focus position, and the focus motor 12 is driven at a low speed (speed V2, V2 <V1) (S3-8), thereby facilitating the focus control in the vicinity of the focus position. The focus accuracy is improved.
[0029]
In step (S3-5), if a> (a '+. DELTA.k) is not satisfied (NO in S3-5), and if a <(a'-. DELTA.k) is not satisfied (NO in S3-9), focus lens 2 is set. Return to the step (S3-2) so as to further advance (forward direction), and if a> (a '+. DELTA.k) but not (NO in S3-5) and a <(a'-. DELTA.k) ( In S3-9 (YES), the focus lens 2 is moved in the opposite direction (S3-10), and then the focus lens 2 is moved out and returns to step (S3-2).
[0030]
FIG. 7 is a timing chart of obtaining and comparing evaluation values and driving a focus motor in the third embodiment. When the focus motor 12 is driven at a high speed (hereinafter, referred to as a high-speed drive mode), the CPU 11 Acquisition of an evaluation value and comparison operation are performed for each field, and as a result, if it has decreased, the drive of the focus motor 12 is reversed.
[0031]
In this case, the focus evaluation value to be compared is, for example, a value every three fields in consideration of the influence of flicker. That is, as shown in FIG. 7C, the focus evaluation value (k + n + 3) of the (k + n + 3) field is compared with the data (k + n) three fields before. The drive of the focus motor 12 is controlled based on the comparison result. In this way, when the focus motor 12 is driven at a high speed, the focus evaluation is performed even when it is determined that the focus motor 12 is not near the in-focus position although it is actually near the in-focus position and is driven at a high speed. The amount of overrun at the position where the value becomes the maximum can be reduced, the unsightlyness of the shot image until focusing can be reduced, and the focusing time can be shortened.
[0032]
On the other hand, when it is near the focus position, taking into account the influence of flicker, a focus evaluation value is obtained and calculated at three-field intervals, for example, and the focus motor 12 is driven at a low speed. As a result, in the vicinity of the focus position, the amount of overrun of the focus position can be minimized, and the stop at the accurate focus position is possible.
[0033]
Also, as shown in FIG. 7, in the case of the high-speed drive mode, for example, when six-step drive is required, instead of driving six steps at a time, each drive is synchronized with a VD (Vertical Drive) cycle. By driving the focus motor 12 with the movement amount limited to two steps for each VD, the evaluation values to be compared (for example, (k), (k + 3), and (k + n) in FIG. 7) (k + n + 3)), the effect of motor drive can be reduced, so that a highly accurate comparison can be made, and a decrease from the peak value can be detected reliably and quickly.
[0034]
In order to avoid the influence of noise, the means for reversing the focus motor 12 reliably determines the decrease in the focus evaluation value (that is, the direction away from the focus position) by detecting the decrease of the evaluation value twice in succession. Is effective in 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 subject (that is, a good S / N ratio), 1 There is sufficient reliability only by the detection of the times.
[0035]
Therefore, in the high-speed drive mode, for example, when a stepping motor is used as the focus motor 12, the result of the comparison of the evaluation values is that the drive is not in the vicinity of the in-focus position but is required to be performed in six steps (actually, Depending on the focus lens position, the focus position may be overrun when driven by 6 steps). If the first step is driven as 3 steps and the resulting focus evaluation value decreases for the first time, The next step is driven as one minimum step, and the decrease is determined.
[0036]
As described above, as described above, even when it is determined that six-step driving is necessary, there is a case where the six steps are not actually required, and when a decrease is detected in the first three steps, the next step is performed. This is because there is a high possibility that a decrease is detected in one driving step. By doing so, it is possible to reliably detect a decrease in the evaluation value and reduce unnecessary overrun.
[0037]
When a DC motor other than the stepping motor is used, a similar effect can be obtained by controlling the driving speed instead of controlling the number of steps.
[0038]
In each embodiment, the control signal output to the focus motor control circuit 13 is performed by the CPU 11 and the calculation is performed by the calculation circuit 10 in the configuration of FIG. 2, but the calculation is performed by software of the CPU 11. This is easy, and with such a configuration, the arithmetic circuit 10 can be omitted.
[0039]
【The invention's effect】
As described above, according to the configuration of the first aspect, the focus control device of the present invention detects an increase / decrease in the ratio of the luminance component in two different frequency bands and an increase / decrease in one of the luminance components, and detects those increase / decrease. The drive speed of the focus motor in the vicinity of the in-focus position and in the out-of-focus position is controlled based on the detection result (evaluation value), and the focus lens is driven at high speed in the out-of-focus position. Compared to the position, the focus lens is driven at a lower speed, and the focus value is exceeded by acquiring and evaluating the evaluation value based on the judgment of out-of-focus and in-focus in a longer cycle. The amount of run can be suppressed, and the focus lens can be stopped at an accurate focusing position, so that both the focusing speed and the focusing accuracy can be improved.
[0040]
According to the configuration of the second aspect, the threshold value for detecting an increase in the luminance component is made different from the threshold value for detecting the maximum value after the increase in the luminance component, so that noise or the like is generated at an out-of-focus position. Erroneous determination of the increase or decrease of the evaluation value due to the above can be reduced, and the overrun amount at the focus position can be reduced near the focus position, so that the focus speed can be improved.
[0041]
According to the configuration of the third aspect, at the time of the high-speed driving, the focus lens is gradually moved by a predetermined amount to a required movement amount in synchronization with the cycle of the acquisition of the evaluation value and the comparison operation, so that the comparison object can be obtained. Thus, the influence of the driving of the focus motor on the evaluation value can be reduced, high-precision comparison can be performed, and the focus position can be detected quickly and reliably.
[0042]
According to the configuration of the fourth aspect, at the time of the high-speed drive, the drive is not immediately performed until the required focus lens movement amount obtained from the result of the comparison operation of the evaluation values, and the predetermined movement is performed in the first drive step. When the movement is reduced by the amount and the result is compared with the evaluation value based on the result, when it is determined that the position is near the focus position (when the focus position is determined twice consecutively near the focus position), the operation is shifted to the low-speed drive with the smaller movement amount. By doing so, the focus position can be reliably detected, and overrun of the focus position can be prevented.
[Brief description of the drawings]
FIG. 1 is a flowchart relating to focus motor control in a first embodiment of a focus control device of the present invention.
FIG. 2 is a block diagram illustrating 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 diagram illustrating a relationship between a ratio of evaluation values and a focus lens extension amount.
FIG. 5 is a flowchart related to focus motor control according to a 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 timing chart of acquisition of an evaluation value, comparison operation, and driving of a focus motor according to a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image pickup lens system, 2 ... Focus lens, 3 ... Image sensor, 4 ... Camera process part, 5 ... Video signal processing circuit, 6, 7 ... Band pass filter, 8, 9 ... Integrator circuit, 10 ... Operation circuit, 11 ... CPU, 12 ... focus motor, 13 ... focus motor control circuit.

Claims (4)

Obtaining a focus signal from the change of the luminance component of the video signal obtained by imaging, the ratio of the luminance component of the line the Hare focal controller focus control based on the focus signal, any two different frequency bands A means for detecting an increase or decrease in the luminance component, a means for detecting an increase or decrease in the luminance component of one frequency band, and a ratio of the luminance components of any two different frequency bands does not increase based on the detection results of the two means, and A focus position determining unit that determines that the position is near the focus position when only the luminance component of one frequency band increases, and otherwise determines that the focus position is a non-focus position; Accordingly, when it is determined that out-of-focus position, and sets the driving speed of the focus motor for driving the focus lens to a predetermined speed, the line a comparison operation and acquisition of the detection result at a predetermined cycle , When it is determined that the focus position vicinity, as well as the driving speed of the focus motor slower than the predetermined speed, and means for performing comparison operation between the result of detection obtained at the predetermined period longer than the period focus point controller you characterized in that the. A means for changing the relationship between a threshold value for detecting an increase in the luminance component and a threshold value for detecting the maximum value after detecting the increase between the vicinity of the in-focus position and the out-of-focus position focal control device according to claim 1, wherein the a. 2. The focus control according to claim 1 , wherein the drive speed of the focus motor is limited to a predetermined focus lens movement amount for each cycle in synchronization with a cycle of the acquisition of the detection result and the comparison calculation. apparatus. Wherein the immediately after the determination of the position near the focus has been made on the first detection result, by the time the subsequent same determination has been made, according to claim 1 or, characterized in gradually to the driving speed of the focus motor to the low speed 3 focus point control apparatus according.

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