JP2004070037A - Automatic focusing device - Google Patents

Abstract

An object of the present invention is to provide an automatic focus adjustment device capable of capturing a high-quality moving image or a high-definition still image without missing a photo opportunity.
A focus detection circuit detects a focus signal by extracting a medium-high frequency component from a video signal, a focus direction determination circuit determines a focus direction from a time-varying component of the focus signal, and a focus direction determination circuit. A focus direction memory 504 for storing the direction, a focus vicinity determination circuit 505 for determining whether or not the focus is near the focus based on the level of the focus signal VF and the distribution state of the focus direction, and a focus signal VF. A lens control amount calculating circuit 503 for determining the moving direction and the moving amount of the lens based on the proximity determination result, and a lens driving unit 6 for driving the focus adjusting lens 1a according to the output of the lens control amount calculating circuit 503. In the vicinity of focusing, the movement amount of the lens is reduced or set to zero in the vicinity of focusing, so that an automatic focusing device with high quality, high responsiveness and high accuracy can be obtained.
[Selection] Fig. 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus adjustment using an image signal obtained by shooting in an imaging apparatus such as a video camera or a digital still camera, and more particularly to an automatic focus adjustment apparatus that automatically adjusts an image of a subject to be shot to an optimum focus position. It is about.
[0002]
[Prior art]
For an image pickup apparatus such as a video camera or a digital still camera, an automatic focus adjustment function (autofocus function) is one of important functions for improving operability. Several methods and apparatuses for realizing the functions have already been proposed and implemented. A typical example is the so-called “hill climbing method”. In this method, a medium-high frequency component is extracted from a video signal obtained by photographing, and the position of a lens is controlled so that the level thereof becomes maximum (or maximum). This method is based on the principle that the circle of confusion increases as the lens moves away from the focal position, and thus the contrast of the subject image formed via the lens decreases as the distance from the focal position increases. The medium high frequency component of the video signal is a signal corresponding to the degree of contrast of the subject image.
[0003]
This method is classified as a passive method, and does not require a special light-emitting device such as an active method such as an "infrared ray method". In addition, it is hardly affected by the subject distance, so it is possible to adjust the focus with high accuracy. Have. Further, since the video signal itself is used, another optical system provided in a system called “phase difference detection system” is not required even in the same passive system. Therefore, it is suitable for cost reduction and size reduction.
[0004]
On the other hand, low-contrast subjects where the focus signal level is relatively low, mixed scenes where there are multiple local maxima in the focus signal, and low-light scenes that are susceptible to the noise of the video signal , Subjects and scenes that are not good in principle.
[0005]
As a measure against a low-contrast subject or a scene under low illuminance, for example, two kinds of focus signals are extracted in different frequency bands from a high-frequency component to be extracted from a video signal, and the situation of the subject is determined according to a signal level or the like. A method of selectively using the signal as a signal of a hill-climbing operation is considered.
[0006]
As a measure for a mixed perspective scene, a method of avoiding a mixed perspective by limiting the detection area of the focus signal to a partial range of the screen can be considered. As a countermeasure against noise, a noise level is determined in advance based on a focus signal when there is no contrast, and when the focus signal is lower than the noise level, the lens is moved larger or a minute vibration (hereinafter referred to as wobbling). ) To extract the fluctuation component of the focus signal to specify the focusing direction.
[0007]
Hereinafter, a conventional configuration of a hill-climbing automatic focus adjustment device will be described with reference to the drawings.
[0008]
FIG. 5 shows the configuration of a conventional automatic focusing device. In FIG. 5, the position of the photographing lens 1 composed of a plurality of lenses having a focus adjustment lens 1a is controlled by a lens driving unit 6 (for example, a stepping motor and its driving circuit). An optical image of a subject is formed via an imaging lens 1 on an image pickup device 2 (for example, a CCD) serving as an image pickup unit.
[0009]
The imaging element 2 photoelectrically converts the formed subject image and outputs the time-series signal. The video signal generation circuit 3 performs various kinds of signal processing on the output of the imaging element 2 and outputs a predetermined video signal CO (for example, an NTSC signal). Here, the various signal processing means analog / digital conversion, gain control, γ correction, luminance signal generation processing, color difference signal generation processing, and the like, and further includes aperture correction, noise reduction, and the like as necessary.
[0010]
The focus signal detection circuit 4 integrates the luminance signal YE of the time-series signal output from the video signal generation circuit 3 with a low-frequency band-pass filter 41 (hereinafter, referred to as LPF) to remove noise components. It outputs a BP signal differentiated by a high-frequency band-pass filter 42 (hereinafter referred to as HPF). After converting this signal into an absolute value, the peak detection circuit 43 detects the peak value (PK signal) of a signal corresponding to a preset area (for example, 50% at the center of the photographing screen) every horizontal scanning period. Further, the peak value is cumulatively added by the adding circuit 44 over the vertical scanning period to generate the focus signal VF. This focus signal VF becomes a field representative value corresponding to the degree of contrast of the subject image.
[0011]
Here, FIG. 6 is a schematic diagram showing an image of the operation of detecting the focus signal VF from the photographing screen by the focus signal detection circuit 4, and FIG. 6 shows an example of a subject having vertical stripes of “black and white”. 4A to 4D show the blurred state of the subject, and FIGS. 4E to 4H show the focused state of the subject.
[0012]
First, when the subject is out of focus as shown in FIG. 6A, the signal level in the horizontal scanning period of the detection area 32, which is an area of approximately 50% in the center on the photographing screen 31, is detected by the HPF 42. The differentiated BP signal is as shown in FIG. When this signal is converted into an absolute value by the peak detection circuit 43, the result becomes as shown in FIG. 6C, and the peak value (PK signal) at that time is output to the addition circuit 44. In FIG. 6D, the peak value is indicated by a thin line arrow, and the length indicates the magnitude of the peak value. Similarly, the peak value is detected for every horizontal scanning period in the detection area 32, and the sum is added by the adding circuit 44 for the vertical scanning period to obtain a focus signal VF. FIG. 6D shows the magnitude of the focus signal VF by a thick arrow. The length of the thick arrow indicates the magnitude of the focus signal VF.
[0013]
Next, when the object is in focus as shown in FIG. 6E, the signal level of the detection area 32 in the horizontal scanning period, which is an area of approximately 50% in the center on the shooting screen 31, is The BP signal detected and differentiated by the HPF 42 is as shown in FIG. When this signal is converted into an absolute value by the peak detection circuit 43, the result is as shown in FIG. 6G. The peak value (PK signal) at that time is output to the addition circuit 44. In FIG. 6H, the peak value is indicated by a thin arrow, and the length indicates the magnitude of the peak value. Similarly, the peak value is detected for every horizontal scanning period in the detection area 32, and the sum is added by the adding circuit 44 for the vertical scanning period to obtain a focus signal VF. FIG. 6H shows the magnitude of the focus signal VF by a thick arrow. The length of the thick arrow indicates the magnitude of the focus signal VF.
[0014]
As can be seen from a comparison between FIGS. 6B and 6F, there is a difference in the signal level detected by the HPF 42 between the blurred state and the in-focus state. Of course there is a difference. As shown, the focus signal VF is larger in the focused state than in the blurred state.
[0015]
Returning to FIG. 5, the lens control circuit 5 generates a fluctuation component ΔVF by taking a difference between the focus signal VF and a past focus signal, for example, a focus signal obtained one field before, by the difference circuit 501. The focusing direction determination circuit 502 determines whether the focusing direction is far or near with respect to the current time, or the same as or opposite to the immediately preceding moving direction, based on the sign of the variation component ΔVF. The lens control amount calculation circuit 503 adds a predetermined movement amount in the moving direction and outputs the result to the lens driving unit 6 as a lens control amount. The lens driving unit 6 drives the focus adjusting lens 1a based on the control amount. Focus adjustment is automatically performed by these configurations and operations.
[0016]
[Problems to be solved by the invention]
Here, the lens movement amount in the lens control amount calculation circuit 503 in the lens control circuit 5 will be described in more detail.
[0017]
If the amount of movement of the focusing lens 1a is increased, the moving speed of the focusing lens 1a increases. However, if the moving speed is too fast, the stepping motor may not be able to correspond to the lens control amount and the corresponding moving position, which may cause a so-called step-out phenomenon. If the amount of movement of the focus adjusting lens 1a is too large, a hunting phenomenon in which the focus shifts largely in the vicinity of the focus is conspicuous, and the image quality is significantly impaired. Conversely, if the amount of movement is too small, it takes a long time to reach the in-focus position, resulting in poor responsiveness.
[0018]
Therefore, a method of determining the lens movement amount based on the level of the focus signal VF can be considered. FIG. 7 shows a hill-climbing curve of the focus signal VF that changes depending on the subject. In FIG. 7, the X axis indicates the lens position of the focus adjusting lens 1a, and the focal position is indicated at substantially the center. The Y axis indicates the level of the focus signal VF. The characteristics of the subject A indicate the characteristics when the shooting conditions of the subject are good (the state where the contrast and the illuminance are sufficient), and the characteristics of the subject B indicate the state where the shooting conditions of the subject are poor (the low contrast, the low illuminance, and the like). LEV1 and LEV2 indicate threshold levels, and MV1 to MV3 indicate lens movement amounts. For example, as shown in FIG. 6, a threshold level LEV1 and a threshold level LEV2 (LEV2> LEV1) are preset, and the relationship between the noise level LEV1, the threshold level LEV2, and the focus signal VF is as follows.
VF <LEV1
If so, set the movement amount to MV1,
LEV1 ≦ VF <LEV2
Then, set the movement amount to MV2,
LEV2 ≦ VF
If so, the moving amount is set to MV3. Here, the relationship between the movement amounts MV1 to MV3 is
MV1>MV2> MV3
And In FIG. 7, the movement amounts of MV1 to MV3 are indicated by the lengths of arrows.
[0019]
In FIG. 7, for example, in the case of the subject A, when the lens position is P1, the focus signal VF is less than LEV1, and the lens moves toward the in-focus position by the movement amount MV1. When the lens moves toward the focus position and the level of the focus signal VF rises and exceeds LEV1 (the lens position at this time is P2), the lens is switched to MV2, which is a movement amount smaller than the movement amount MV1, and moves to the focus position. Move towards. Further, when the level of the focus signal VF exceeds LEV2 (the lens position at this time is P3), the focus signal VF is switched to MV3 having a smaller moving amount than MV2 and moves. When the lens is moved to P4, which has passed the focus position, the level of the focus signal VF is lowered. Next, the lens is moved in the opposite direction, and the lens is moved closer to the focus position. The position where the level of the focus signal VF becomes highest is the focus position. As described above, by changing the amount of movement of the focus adjustment lens 1a according to the level of the focus signal VF, the above problem is solved.
[0020]
However, since the level of the focus signal VF differs depending on the condition (contrast, illuminance, etc.) of the subject even when the subject distance is the same, the focus adjusting lens 1a is located near the focus, for example, as in the subject B in FIG. Therefore, even though the focus signal VF is equal to or higher than the threshold level LEV2, the moving amount is not the moving amount MV3 but the moving amount MV2 larger than the MV3, and the quality of the video (moving image) may be deteriorated due to hunting.
[0021]
On the other hand, when shooting a high-definition still image using the still image shooting function of a digital still camera or a video camera, the subject image captured with the shutter released may be the subject image exposed with the lens stopped. This is desirable in terms of resolution and the like, and the higher the number of pixels of a still image, the higher the resolution required, so that the focusing accuracy becomes severe.
[0022]
FIG. 8 is a schematic diagram illustrating the lens movement behavior in the case of the subject B shown in FIG. 7, in which the horizontal axis represents the time until the lens stops and the vertical axis represents the lens position. In the conventional configuration, the stopping accuracy of the lens greatly depends on the predetermined lens moving amount (MV1 to 3), and the moving amount cannot be reduced for the same reason as for a moving image. (Especially resolution).
[0023]
As a measure for improving the focusing accuracy at the time of shooting a still image, the configuration is such that the release button can be detected in two stages, a half-pressed state and a full-pressed state, and the lens is moved when the half-pressed state is pressed to search for the maximum value of the focus signal. A so-called “scan method” may be employed, but in this case, a time lag occurs between when the photographer presses the release button and when the subject is actually imaged, so that a shutter chance is missed. There's a problem.
[0024]
In view of the foregoing, the present invention provides automatic focusing with excellent responsiveness, stability, accuracy, and quality in order to always provide high-quality moving images and high-resolution still images without image distortion due to hunting. It is intended to provide a device.
[0025]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a photographing lens including a focusing lens, an image pickup unit for performing photoelectric conversion of a subject image formed through the photographing lens, and a predetermined signal processing for an output of the image pickup unit. Video signal generating means for generating a video signal by performing the processing, a focus signal detecting means for extracting a predetermined frequency band from the video signal and detecting a focus signal indicating the degree of contrast of the subject at predetermined time intervals, A focus direction judging means for judging a focus direction from an increase or a decrease in a time-varying component of a focus signal and outputting a focus direction signal indicating a far side or a near side; and a focus for storing a plurality of the focus direction signals. Direction storage means, focus vicinity determination means for determining whether or not the current lens position is near focus from the level of the focus signal and the distribution state of the plurality of focus direction signals, and the focus signal detection means Before output A lens control amount calculating unit that determines a moving direction and a moving amount of the lens based on a focus signal and a determination result of the focusing proximity determining unit; and a focusing lens according to an output of the lens control amount calculating unit. Lens driving means for driving or stopping.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
According to a first aspect of the present invention, the photographing lens includes a focus adjusting lens, the image pickup means photoelectrically converts a subject image formed through the image pickup lens, and the image signal output means outputs the image pickup means. A predetermined signal processing is performed to generate a video signal, a predetermined frequency band is extracted from the video signal by the focus signal detection unit, and a focus signal indicating a degree of contrast of the subject is detected at predetermined time intervals, The focusing direction is determined by an increase or decrease in the time-varying component of the focus signal by the focusing direction determination unit, a focusing direction signal indicating a far side or a near side is output, and the focusing direction signal is determined by the focusing direction storage unit. A plurality of stored and determined by the in-focus vicinity determining means whether or not the current lens position is near the in-focus state from the distribution state of the plurality of focusing direction signals, and the in-focus signal detecting means by the lens control amount calculating means. of The moving direction and the moving amount of the lens are determined based on the focus signal to be applied and the determination result of the focusing vicinity determining means, and the focus adjusting lens is determined by a lens driving means in accordance with an output of the lens control amount calculating means. By driving or stopping, a high-precision, high-quality automatic focusing device that is always stable and has good responsiveness is realized.
[0027]
The invention according to claim 2 is to reduce the amount of movement of the lens during the period in which the lens control amount calculating unit determines that the in-focus state is near the in-focus state as compared with the outside of the period. Responsiveness and accuracy are improved.
[0028]
According to the third aspect of the present invention, the responsiveness is further improved by setting the movement amount of the lens to zero when the in-focus vicinity determination means determines that the lens is in the vicinity of focus by the lens control amount calculation means. .
[0029]
According to a fourth aspect of the present invention, the in-focus vicinity determination is performed by the in-focus vicinity determination means by determining that the in-focus vicinity is obtained only when the in-focus direction signal becomes a predetermined number of times on the far side and the near side respectively. Since the accuracy is improved, responsiveness and accuracy are stably improved without malfunction.
[0030]
According to a fifth aspect of the present invention, the in-focus vicinity determining means determines whether or not the focus signal is in the vicinity of focus only when the focus signal is equal to or higher than a predetermined level in consideration of the level of the focus signal. Accuracy of determination is improved, and responsiveness, accuracy, and quality are stably improved without malfunction.
[0031]
Hereinafter, an embodiment of an automatic focusing device of the present invention will be described with reference to the drawings.
[0032]
(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of an embodiment of the automatic focusing apparatus according to the present invention. In FIG. 1, components having the same configuration and function as those of FIG. 5 already described are denoted by the same reference numerals. Reference numeral 1 denotes a photographing lens including a plurality of lens groups, which has a configuration in which a zoom lens, a focus lens, and the like are arranged on the optical axis. Reference numeral 1a denotes a focus adjustment lens which is a part of the photographing lens 1, and can perform focus adjustment by moving the lens in the optical axis direction. Reference numeral 2 denotes an imaging device which is an imaging device which forms an optical signal of a subject incident through the photographing lens 1, converts the optical signal into an electric signal, and outputs the electric signal as a time-series signal, for example, from a solid-state imaging device such as a CCD (Charge Coupled Device). Become. Reference numeral 3 denotes a video signal generation circuit which is a video signal generation means for performing various signal processing on an output signal from the image sensor 2. The various signal processing includes analog / digital conversion, gain control, γ correction, luminance signal generation processing, color difference Refers to signal generation processing and the like, and performs aperture correction, noise reduction, and the like as necessary.
[0033]
Reference numeral 4 denotes a focus signal detection circuit, which is a focus signal detection means, and includes a low frequency band filter (hereinafter, referred to as LPF) 41, a high frequency band filter (hereinafter, referred to as HPF), a peak detection circuit 43, and an addition circuit 44. Is done. The LPF 41 integrates a luminance signal in the time-series signal output from the video signal generation circuit 3 to remove a noise component. The HPF 42 differentiates the output signal from the LPF 41 and outputs it (BP signal). After converting the signal from the HPF 42 into an absolute value, the peak detection circuit 43 detects the peak value (PK signal) of the signal corresponding to a preset area (for example, 50% at the center of the shooting screen) every horizontal scanning period. I do. The adder circuit 44 accumulatively adds the peak values of the signal from the peak detection circuit 43 over the vertical scanning period to generate a focus signal VF.
[0034]
Reference numeral 5 denotes a lens control circuit which is a lens control means. The difference signal 501 is obtained by subtracting the focus signal VF from a past focus signal, for example, a focus signal obtained one field before, by a difference circuit 501 which is a difference means. Generate. The focusing direction determination circuit 502, which is a focusing direction determination unit, determines whether the focusing direction is far side or near side with respect to the current time, or the same as or opposite to the immediately preceding moving direction by looking at the sign of the fluctuation component ΔVF. to decide. At this time, when the lens driving accompanied by the wobbling operation is performed for the direction determination, if the wobbling frequency is 30 Hz, the vibration becomes one period in two fields, so that the focus signal obtained one field before is used. After the difference of (1), the result of inverting the sign alternately for each field is used for the focus direction determination. In the direction determination, if the sign is positive, the far side is the focusing direction, and if the sign is negative, the near side is the focusing direction.
[0035]
The focus direction determination memory 504 stores a plurality (for example, 20) of the results determined by the focus direction determination circuit 502 in chronological order. The newest 20 pieces of data are always stored by overwriting the oldest data in the order of more than 20 pieces.
[0036]
The focus vicinity determination circuit 505 serving as focus vicinity determination means evaluates these 20 focus direction data to determine whether or not the focus is in the vicinity of focus. As a determination method, for example, 20 data are counted for each direction, and if each direction is a predetermined threshold value (for example, 5 or more on the far side and 5 or more on the near side), it is determined that the focus is near.
[0037]
A lens control amount calculation circuit 503 serving as a lens control amount calculation means determines the moving direction of the lens from the result obtained by the focus direction determination circuit 502, and determines the level of the focus signal VF and the result of the focus vicinity determination circuit 505. , And outputs the lens moving amount to the lens driving unit 6. The lens driving unit 6 is driven by the control amount to move the focus adjusting lens 1a. Focus adjustment is automatically performed by these configurations and operations.
[0038]
With these configurations and operations, it is possible to adaptively change the amount of movement of the lens depending on whether it is in the vicinity of focus. The lens control circuit 5 includes a difference circuit 501, a focus direction determination circuit 502, a lens control amount calculation circuit 503, a focus direction memory 504, and a focus proximity determination circuit 505.
[0039]
The operation of the thus-configured automatic focusing apparatus of the present embodiment will be described below.
[0040]
The position of the photographing lens 1 composed of a plurality of lenses having a focusing lens 1a is controlled by a lens driving unit 6 (for example, a linear motor and its driving circuit).
[0041]
An optical image of a subject is formed via an imaging lens 1 on an image pickup device 2 (for example, a CCD) serving as an image pickup unit. The imaging element 2 photoelectrically converts the formed subject image and outputs the time-series signal. The video signal generation circuit 3 performs various kinds of signal processing on the output of the imaging element 2 and outputs a predetermined video signal CO (for example, an NTSC signal). Here, the various signal processing means analog / digital conversion, gain control, gamma correction, luminance signal generation processing, color difference signal generation processing, and the like, and further performs aperture correction, noise reduction, and the like as necessary.
[0042]
The focus signal detection circuit 4 integrates the luminance signal YE of the time-series signal output from the video signal generation circuit 3 by the LPF 41 to remove a noise component, and then outputs a BP signal differentiated by the HPF 42. After converting this signal into an absolute value, the peak detection circuit 43 detects the peak value of a signal corresponding to a preset area (for example, 50% at the center of the photographing screen) every horizontal scanning period, and further detects the vertical value. The peak value (PK signal) is cumulatively added by the adding circuit 44 over the scanning period to generate the focus signal VF. This focus signal VF becomes a representative value corresponding to the degree of contrast of the subject image, and is input to the lens control circuit 5.
[0043]
Here, the determination of the lens movement amount in the lens control amount calculation circuit 503 in the lens control circuit 5 will be described in detail.
[0044]
As a method of determining the movement amount of the lens based on the focus signal VF, for example, a threshold level LEV1 and a threshold level LEV2 (LEV2> LEV1) are set in advance,
VF <LEV1
If so, the movement amount MV1,
LEV1 ≦ VF <LEV2
If so, the movement amount MV2,
LEV2 ≦ VF
If so, the movement amount is MV3. Further, when the focus vicinity determination circuit 505 determines that the focus is near the focus, the movement amount is set to MV4. Here, the relationship between the movement amounts MV1, MV2, MV3, MV4 is
MV1>MV2>MV3> MV4.
MV4 is, for example, a minimum unit amount.
[0045]
Next, the relationship between the focus signal VF and the lens movement will be described with reference to FIG.
[0046]
In FIG. 2, the X axis indicates the lens position of the focus adjustment lens 1a, and the focus position is indicated at substantially the center. The Y axis indicates the level of the focus signal VF. The characteristics of the subject A indicate the characteristics when the shooting conditions of the subject are good (the state where the contrast and the illuminance are sufficient), and the characteristics of the subject B indicate the state where the shooting conditions of the subject are poor (the low contrast, the low illuminance, and the like). LEV1 and LEV2 indicate threshold levels, and MV1 to MV4 indicate lens movement amounts. In the figure, the movement amount of MV1 to MV4 is represented by the length of the arrow.
[0047]
In FIG. 2, for example, in the case of the subject A, when the lens position is P1, the focus signal VF is less than LEV1, and the lens moves toward the in-focus position by the movement amount MV1. When the lens moves toward the focus position and the level of the focus signal VF rises and exceeds LEV1 (the lens position at this time is P2), the lens is switched to MV2, which is a movement amount smaller than the movement amount MV1, and moves to the focus position. Move towards. Further, when the level of the focus signal VF exceeds LEV2 (the lens position at this time is P3), the focus signal VF is switched to MV3 having a smaller moving amount than MV2 and moves. When the lens reaches the position P4, the focus vicinity determination circuit 505 determines that the current lens position is near the focus, and switches the movement amount to MV4 smaller than MV3. The method of determining the vicinity of the focus will be described later with reference to FIG. Next, the lens is moved by the moving amount of MV4, and when the lens is moved to P5 after passing through the focus position, the level of the focus signal VF decreases. Next, the lens is moved in the opposite direction, and the lens is moved to the focus position. Approaching. The position where the level of the focus signal VF becomes highest is the focus position.
[0048]
Next, in the case of the subject B, when the lens position is Q1, the focus signal VF is less than LEV1, and the lens moves toward the in-focus position by the movement amount MV1. When the lens moves toward the focus position and the level of the focus signal VF rises and exceeds LEV1 (the lens position at this time is Q2), the lens is switched to MV2, which is a movement amount smaller than the movement amount MV1, and moves to the focus position. Move towards. When the lens position reaches Q3, the near focus determination circuit 505 determines that the current lens position is near focus and switches the movement amount from MV2 to MV4. The method of determining the vicinity of the focus will be described later with reference to FIG. Next, when the lens is moved by the moving amount of MV4, and the lens is moved to Q4 after passing through the focusing position, the level of the focus signal VF is lowered. Approaching. The position where the level of the focus signal VF becomes highest is the focus position.
[0049]
As described above, according to the present embodiment, since the movement of the lens in the vicinity of the focus is minimized without depending on the subject, it is possible to minimize disturbance of the image due to hunting.
[0050]
If MV4 is set to zero, the lens is immediately stopped when it comes near the in-focus state, so that a stable image without hunting can be provided.
[0051]
Further, by providing the movement amount MV4 for the vicinity of focusing, it is possible to set MV1, MV2, and MV3 to values larger than before. This makes it possible to increase the moving speed of the lens at a position that is not near the in-focus state, thereby improving the response.
[0052]
Further, in the case where hill-climbing control is performed with wobbling operation, if the in-focus vicinity determination result is determined to be near the in-focus state, the amplitude amount of the wobbling is further reduced so that the in-focus state is also reduced. Can be reduced.
[0053]
If the focus is not in the vicinity of the focus, the amplitude of the wobbling can be set larger than before, so that the fluctuation component of the focus signal can be easily extracted, and the focus direction can be easily determined. This makes it possible to focus with good responsiveness even in a conventional scene or a subject where the hill-climbing method is poor, such as a low-illuminance or low-contrast subject.
[0054]
The amount of wobbling amplitude is added to the amount of lens movement and output to the lens driving unit 6 as a lens control amount.
[0055]
Next, with reference to FIG. 3, the details of the process in which the focus vicinity determination circuit 505 determines that the lens position is near the focus using the subject B in FIG. 2 as an example will be described together with the behavior of the lens.
[0056]
In the schematic diagram of the lens movement in FIG. 3, the X axis indicates time, and the Y axis indicates the lens position. The operation will be described with the passage of time in the figure. First, in FIG. 3A, the lens is moved toward the in-focus position by the movement amount MV1. Since the focusing direction at this time is the positive direction from the start of the movement, the sign is the positive direction (+ direction) as shown in FIG. Therefore, the number of codes recorded in the focusing direction memory 504 is 20 for + and 0 for-. Next, when the focus signal VF exceeds LEV1, the moving amount is switched from MV1 to MV2, and when the lens continues to move and exceeds the focusing position, the focusing direction becomes a negative direction. 502 outputs a minus sign. The-sign is stored in the focusing direction memory 504, and the lens passes through the focusing position again at the timing when four-signs are stored. Then, the sign output from the focusing direction determination circuit 502 becomes + again, and the number of + is added. Such operations are repeated, and when five minus signs are stored in the focus direction memory 504, it is determined that the lens is located near the focus, and the movement amount MV2 is switched to MV4. After that, the lens is moved toward the in-focus position by the movement amount of the MV4.
[0057]
The lens control amount calculation circuit 503 sets the focus at a timing (Z2 in FIG. 3) at which a predetermined time has elapsed from the timing (Z1 in FIG. 3) at which the focus proximity determination circuit 505 determines that the lens position is near the focus. The operation is stopped regardless of the lens position of the adjusting lens 1a. When the lens is stopped, the focusing state may stop slightly with the lens position shifted from the focusing position, but since the lens movement amount immediately before stopping the lens is extremely small, it is as close as possible to the focusing position. Since the focus adjusting lens 1a can be stopped at the position, there is a possibility that an image may be slightly out of focus, but this is a level at which there is no problem in image quality.
[0058]
As described above, according to the present embodiment, the lens is moved at the MV1 having the largest movement amount when the focus is not in the vicinity of focus, so that the speed of the lens can be increased. Is moved with a small MV4, it is possible to control such that the movement of the lens is slow (fine), thereby achieving high responsiveness, stability, accuracy and quality with high performance.
[0059]
Furthermore, since the shooting style and the required accuracy are different between video shooting and still image shooting, different moving amounts are provided for video and still images, and the balance of focusing performance is customized to the optimal state for each. It is also possible.
[0060]
The number stored in the focusing direction memory 504 is not limited to the above value (20). If the number is smaller than 20, the size of the memory can be reduced. Conversely, if the number of movements is increased, the moving amount MV2 or the moving amount MV3 is large, and there is an advantage that the in-focus vicinity determination can be performed stably even if the wobbling is performed across the in-focus position and the direction determination period is increased.
[0061]
Note that the threshold value used in the in-focus vicinity determination circuit 505 is not fixed to the above value (5 or more in each direction). For example, if the number is larger than five, the influence of noise can be further reduced, and the difference in the period of the focus determination signal due to the difference in the contrast of the subject is easily absorbed, so that the accuracy of the focus determination is improved. Conversely, when the distance is reduced, the speed of the near focus determination is improved, which leads to an improvement in responsiveness.
[0062]
Note that the lens stop at the timing Z2 in FIG. 3 is performed by stopping the lens by controlling the time from the near focus determination timing Z1 to Z2. However, when focusing by wobbling such as when shooting a moving image, the wobbling operation is performed. It may be continued. However, at the time of shooting a still image, if the wobbling operation is performed when the lens is stopped, the image quality deteriorates conspicuously. Therefore, the wobbling operation is stopped.
[0063]
Note that the period management from the focus vicinity determination timing Z1 to the lens stop timing Z2 is performed by time management in the present embodiment, but after the focus vicinity determination timing Z1, the number of + or-in the focus direction memory 504 is determined. The number of times of memory management may be such that the lens stop timing is set when a focus signal having a value equal to or more than a predetermined value (five in the present embodiment) is continuously stored for a predetermined number of times.
[0064]
(Embodiment 2)
Next, a second embodiment of the automatic focusing apparatus of the present invention will be described with reference to the drawings. FIG. 4 shows the configuration of the second embodiment of the present invention.
[0065]
The overall configuration is different from that of the first embodiment in that a lens position detection unit 7 (for example, an MR sensor) is provided, and that a focus signal VF is also connected to the focus vicinity determination circuit 505. The description of the components having the same numbers is omitted here.
[0066]
The lens position detector 7 detects the current lens position, and the lens control circuit 5 controls the next lens moving direction and moving amount while feeding back the current lens position.
[0067]
Since the lens position control is feedback control, the position of the lens can be controlled more quickly and more accurately. This configuration is more effective if, for example, the lens driving unit 6 is a linear motor. That is, since the linear motor can be driven at a higher speed than the stepping motor, the lens control circuit 5 always performs wobbling to detect the focusing direction and performs hill-climbing control to a position where the focus signal VF becomes maximum (maximum). A control method can be adopted.
[0068]
An advantage of constantly wobbling is that, for example, the responsiveness to movement of a subject or a change in a scene is improved, so that the responsiveness when the shooting composition is changed is greatly improved.
[0069]
Even in such a configuration, the adaptive control of the movement amount based on the focus vicinity determination of the present invention is extremely effective, and improves the responsiveness, improves the stability, and increases the accuracy.
[0070]
Further, in the present embodiment, the focus signal VF is also input to the focus vicinity determination circuit. Thereby, the accuracy and reliability of the in-focus vicinity determination are improved. For example, if the focus signal is equal to or lower than the noise level, the focus direction determination result is greatly affected by noise, and the reliability of data is low.
[0071]
【The invention's effect】
As described above, the present invention does not malfunction under a wide range of subject conditions by judging whether or not it is in the vicinity of focus with extremely high accuracy and adaptively changing the amount of lens movement. It enables stable, good responsiveness and highly accurate focus adjustment, and has an extremely excellent effect on automatic focus adjustment.
[0072]
By providing such an automatic focusing device in a video camera or a digital still camera, it is possible to always obtain a stable high-quality moving image and a high-resolution still image with high resolution without missing a photo opportunity.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an automatic focusing apparatus according to a first embodiment of the present invention.
FIG. 2 is an image diagram of a hill-climbing operation by controlling a lens moving amount according to the embodiment of the present invention;
FIG. 3 is a schematic view illustrating a lens behavior in the embodiment of the present invention in the case of the subject 2 in the embodiment.
FIG. 4 is a block diagram illustrating a configuration of an automatic focusing apparatus according to a second embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of a conventional automatic focusing device.
FIG. 6 is a schematic diagram showing an operation image of parfocal signal detection.
FIG. 7 is a schematic diagram showing an image of a hill-climbing operation by conventional lens movement amount control.
FIG. 8 is a schematic view imagining a lens behavior in a conventional example in the case of the subject 2;
[Explanation of symbols]
1 Shooting lens
1a Focusing lens
2 Imaging unit
3 Video signal generation circuit
4 Focus signal detection circuit
5 Lens control circuit
502 Focus direction determination circuit
503 Lens control amount calculation circuit
504 Focus direction memory
505 Focusing vicinity judgment circuit
6 Lens drive

Claims (8)

A photographing lens including a focus adjusting lens, an image pickup unit that performs photoelectric conversion of a subject image formed through the photographing lens, and a video signal generation that performs predetermined signal processing on an output of the image pickup unit to generate a video signal. A focus signal detecting means for extracting a predetermined frequency band from the video signal and detecting a focus signal indicating a degree of contrast of the subject at predetermined time intervals; A focus direction determining means for determining a focus direction and outputting a focus direction signal indicating a far side or a near side; a focus direction storage means for storing a plurality of the focus direction signals; and a plurality of the focus direction signals. Focusing nearness judging means for judging whether or not the current lens position is near the focus from the distribution state of the focus direction signal, and the focus signal output by the focus signal detecting means and the judgment result of the focus nearing judging means. Based on A lens control amount calculating means for determining a moving direction and a moving amount of a lens, and a lens driving means for driving or stopping the focus adjusting lens according to an output of the lens control amount calculating means. Focus adjustment device. 2. The auto-focusing device according to claim 1, further comprising a lens control amount calculating unit that makes the amount of movement of the lens smaller during a period in which the near focus determining unit determines that the focus is close to being in focus. Adjustment device. 2. The automatic focus adjusting device according to claim 1, further comprising a lens control amount calculating unit that sets the amount of movement of the lens to zero when the near focus determining unit determines that the focus is near the focus. 4. The automatic focus determination device according to claim 1, further comprising a focus determination unit that determines that the subject is in focus only when the focus direction signal is equal to or more than a predetermined number of times on the far side and the near side. Focus adjustment device. A photographing lens including a focus adjusting lens, an image pickup unit that performs photoelectric conversion of a subject image formed through the photographing lens, and a video signal generation that performs predetermined signal processing on an output of the image pickup unit to generate a video signal. A focus signal detecting means for extracting a predetermined frequency band from the video signal and detecting a focus signal indicating a degree of contrast of the subject at predetermined time intervals; A focus direction determining means for determining a focus direction and outputting a focus direction signal indicating a far side or a near side; a focus direction storage means for storing a plurality of the focus direction signals; and a level of the focus signal. Only when the value is equal to or greater than a predetermined value, a focus vicinity determining means for determining whether or not the current lens position is near the focus based on a distribution state of the plurality of focus direction signals, and the focus output by the focus signal detecting means. Traffic light A lens control amount calculating unit that determines a moving direction and a moving amount of the lens based on a determination result of the focus vicinity determining unit, and drives or stops the focus adjusting lens according to an output of the lens control amount calculating unit. An automatic focusing device comprising: a lens driving unit. 6. The automatic focusing apparatus according to claim 5, further comprising a lens control amount calculating unit that reduces the amount of movement of the lens during the period in which the in-focus vicinity determining unit determines that the in-focus state is near the in-focus state. Adjustment device. 6. The automatic focus adjustment device according to claim 5, further comprising a lens control amount calculation unit that sets the lens movement amount to zero when the focus vicinity determination unit determines that the focus is near. 8. An automatic focusing apparatus according to claim 5, further comprising a focusing proximity determining means for determining that the subject is in focus only when the focusing direction signal is equal to or more than a predetermined number of times on each of the far side and the near side. Focus adjustment device.

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