JP2004070038A - Auto-focusing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an auto-focusing device excellent in all aspects of responsiveness, stability, precision, and quality in order to constantly provide a high-definition moving picture and a high-resolution still picture without disorder of an image by hunting. <P>SOLUTION: The auto-focusing device is constituted to perform a judgment of near focusing and stop focusing by using data of near focusing. Thus, the responsiveness is improved in the case of not close to focusing, and the quality and precision is improved in near focusing. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL 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 for automatically adjusting an image of a subject to be shot to an optimum focus position. It concerns the device.
[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. 4 shows the configuration of a conventional automatic focusing device. In FIG. 4, 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. 5 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. 5 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 and blurred as shown in FIG. 5A, the HPF 42 detects the signal level in the horizontal scanning period of the detection area 32 which is an area of approximately 50% at the center on the photographing screen 31. 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. 5C, and the peak value (PK signal) at that time is output to the addition circuit 44. In FIG. 5D, 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. 5D 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. 5E, the signal level of the detection area 32 in the horizontal scanning period, which is an area of approximately 50% at 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 becomes as shown in FIG. 5G, and the peak value (PK signal) at that time is output to the addition circuit 44. In FIG. 5H, 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. 5H 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 by comparing FIGS. 5B and 5F, there is a difference in the signal level detected by the HPF 42 between the blurred state and the in-focus state, and the focus signal obtained by cumulatively adding the peak value of this signal is also 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. 4, 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 a 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. 6 shows a hill-climbing curve of the focus signal VF that changes depending on the subject. In FIG. 6, the X-axis indicates the lens position of the focus adjusting lens 1a, and the focal position is substantially at 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. 6, the movement amount of MV1 to MV3 is indicated by the length of the arrow.
[0019]
In FIG. 6, 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, and the like) 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. Although the focus signal VF is equal to or higher than the threshold level LEV1, 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 impaired 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. 7 is a schematic diagram illustrating the behavior of the lens movement in the case of the subject B shown in FIG. 6, 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 an imaging lens including a focusing lens, lens driving means for driving or stopping the focusing lens according to a lens control amount, and an image formed through the imaging lens. Imaging means for photoelectrically converting a subject image; video signal generating means for performing a predetermined signal processing on an output of the imaging means to generate a video signal; and extracting a predetermined frequency band from the video signal to obtain a predetermined time interval. A focus signal detecting means for detecting a focus signal indicating a degree of contrast of a subject for each time; outputting a focus direction signal indicating a far side or a near side by judging a focus direction based on increase / decrease of a time-varying component of the focus signal; Focusing direction determining means, focusing direction storing means for storing a plurality of the focusing direction signals, and focusing proximity determining means for determining whether or not a plurality of the focusing direction signals are in the vicinity of focusing based on a distribution state of the plurality of focusing direction signals. And near-focus data storage for storing the focus signal and the lens control amount as the near-focus focus signal and the near-focus lens control amount during a period in which the near-focus determination unit determines that the focus is near the focus. Means for determining a moving direction and a moving amount of a focus adjusting lens based on the focus signal, the determination result of the near focus determining means, the near focus signal and the near focus lens control amount, A lens control amount calculating means for outputting as a lens control amount, wherein the lens control amount calculating means determines whether the in-focus vicinity data has passed a predetermined time after the in-focus vicinity determining means has determined that the in-focus state is near. The focus adjusting lens is stopped based on the near focus signal and the near focus lens control amount stored in the storage means.
[0026]
Further, when the focus adjusting lens is stopped, a lens control amount calculating means for outputting a lens control amount near the in-focus state at which the focus signal near the in-focus state becomes maximum is output as a lens control amount.
[0027]
In addition, the apparatus further comprises a lens control amount calculating means characterized in that the movement amount of the lens is made smaller during the period in which the focus vicinity determination means determines that the focus is in the vicinity of the focus than in the outside of the period.
[0028]
Further, when the in-focus vicinity determining means determines that the lens is near the in-focus state, the moving amount of the lens is reduced to zero.
[0029]
In addition, during the period in which the focus vicinity determining means determines that the focus is near the focus, the amount of movement of the lens is made smaller than that during the outside of the period. A lens control amount calculating means for outputting a lens control amount for stopping the lens when it is reached is provided.
[0030]
In addition, the apparatus is provided with a focus vicinity determination unit, which determines that the focus is near the 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, respectively.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the first aspect of the present invention, there is provided a photographing lens including a focusing lens, lens driving means for driving or stopping the focusing lens in accordance with a lens control amount, and a lens connected via the photographing lens. Imaging means for photoelectrically converting the image of the imaged subject; video signal generating means for performing a predetermined signal processing on an output of the imaging means to generate a video signal; and extracting a predetermined frequency band from the video signal to obtain a predetermined A focus signal detecting means for detecting a focus signal indicating a degree of contrast of a subject at each time interval; and determining a focusing direction based on increase / decrease of a time-varying component of the focus signal, and determining a focusing direction signal indicating a far side or a near side. A focusing direction determining means for outputting; a focusing direction storing means for storing a plurality of the focusing direction signals; and a focusing neighborhood for determining whether or not the focus state is near from a distribution state of the plurality of focusing direction signals. Judgment means And near-focus data storage for storing the focus signal and the lens control amount as the near-focus focus signal and the near-focus lens control amount during a period in which the near-focus determination unit determines that the focus is near the focus. Means for determining a moving direction and a moving amount of a focus adjusting lens based on the focus signal, the determination result of the near focus determining means, the near focus signal and the near focus lens control amount, A lens control amount calculating means for outputting as a lens control amount, wherein the lens control amount calculating means determines whether the in-focus vicinity data has passed a predetermined time after the in-focus vicinity determining means has determined that the in-focus state is near. The focusing lens is stopped based on the near-focus lens signal and the near-focus lens control amount stored in the storage unit, thereby realizing a high-precision, high-quality automatic focusing device that is stable and responsive at all times. I do.
[0032]
According to the second aspect of the present invention, when the lens for lens control amount is stopped by the lens control amount calculating means, the near-focus lens control amount at which the near-focus focus signal is maximized is output as the lens control amount. This realizes an automatic focusing device with high focusing accuracy.
[0033]
According to a third aspect of the present invention, the lens movement amount is made smaller during the period in which the lens control amount calculating means determines that the focus vicinity is near the focus than in the outside of the period. This realizes an automatic focusing device with high focusing accuracy.
[0034]
According to a fourth aspect of the present invention, when the in-focus vicinity determining means determines that the lens is in the vicinity of the in-focus state by the lens control amount calculating means, the moving amount of the lens is set to zero, thereby providing a more responsive automatic focusing. An adjustment device is realized.
[0035]
According to a fifth aspect of the present invention, the lens moving amount of the lens is reduced during the period in which the lens control amount calculating unit determines that the in-focus state is in the vicinity of the in-focus state, and the in-focus state is reduced. By outputting a lens control amount for stopping the lens when the period determined to be near reaches a predetermined period, an automatic focusing device with good responsiveness and high focusing accuracy is realized.
[0036]
According to a sixth aspect of the present invention, the focus nearing means determines that the focus is near the 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, respectively. Thus, an automatic focusing device having high focusing accuracy can be realized.
[0037]
Hereinafter, an embodiment of an automatic focusing device of the present invention will be described with reference to the drawings.
[0038]
(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. 4 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.
[0039]
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.
[0040]
Reference numeral 5 denotes a lens control circuit, which is a lens control means, which includes a difference circuit 501, a focus direction determination circuit 502, a lens control amount calculation circuit 503, a focus direction memory 504, a focus proximity determination circuit 505, and a focus proximity data memory 506. It has. The difference circuit 501 calculates a difference between the focus signal VF from the adder circuit 44 and a past focus signal (for example, a focus signal obtained one field before) to generate a fluctuation component ΔVF. The focusing direction determination circuit 502 determines whether the focusing direction is far or near, or the same or opposite to the previous moving direction, based on the current time, by checking the sign of the fluctuation component ΔVF from the difference circuit 501. The focus direction memory 504 stores a plurality (for example, 20) of the results determined by the focus direction determination circuit 502 in a time series order. By overwriting the oldest data in order from the oldest data, the latest 20 data are always stored. The focus vicinity determination circuit 505 evaluates the 20 focus direction data stored in the focus direction memory 504 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. The lens control amount calculation circuit 503 moves the focus adjustment lens 1a based on the output of the focus direction determination circuit 502, the level of the focus signal VF, the result of the focus proximity determination circuit 505, and the data of the focus proximity data memory 506. The direction and the movement amount are obtained, and information on the lens control amount is output to the lens driving unit 6. The focus vicinity data memory 506 stores not only the focus signal VF but also the lens control amount for a plurality of past times (for example, 20 times). This stored data is also overwritten sequentially from the oldest data so that the latest 20 times of data are always stored like the focus signal.
[0041]
Reference numeral 7 denotes a lens position detecting unit which is a lens position detecting means, which detects the current lens position on the optical axis of the focus adjusting lens 1a, and comprises, for example, an MR sensor (a magnetoresistive element sensor) and its detection circuit. Information on the current lens position detected by the lens position detector 7 is input to the lens control amount calculation circuit 503.
[0042]
The operation of the thus-configured automatic focusing apparatus of the present embodiment will be described below.
[0043]
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). The lens position detection circuit 7 (for example, an MR sensor and its detection circuit) detects the current lens position on the optical axis of the focusing lens.
[0044]
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.
[0045]
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. A plurality of past focus signals VF (for example, 20 times) are stored in the near focus data memory 506 as near focus signals. The stored data is overwritten from the oldest data so that the latest 20 data are always stored.
[0046]
In addition, the focus vicinity data memory 506 stores not only the focus signal VF but also a lens control amount (described later) from the lens control amount calculation circuit 503 for a plurality of past times (for example, 20 times). Like the focus signal, the stored data is sequentially overwritten from the oldest data so that the latest 20 data are always stored.
[0047]
Here, it is necessary to temporally associate the near-focus focus signal stored in the near-focus data memory 506 with the near-focus lens control amount. As a specific example, the time delay between the output timing of the lens control amount of the lens control unit 5 and the input timing of the focus signal VF to the lens control unit 5 is, for example, 2 when the time interval of the stored data is one field interval. If there is a field, the recording timing in the focus signal memory 506 is delayed by two fields with respect to the recording timing in the near focus data memory 506, and the time is adjusted. Since this corresponds to two data, for example, if the address of the memory is shifted by two, the data is stored in association with the same address.
[0048]
The difference circuit 501 generates a fluctuation component ΔVF by calculating a difference between the focus signal VF and a past focus signal, for example, a focus signal obtained one field before. The focus direction determining circuit 502 determines whether the focus direction is far or near with respect to the current time point, or the same as or opposite to the immediately preceding movement direction, based on the sign (+ or-) of the fluctuation component ΔVF. . 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 (+), for example, it is assumed that the far side is the focusing direction, and if the sign is negative (-), the near side is the focusing direction.
[0049]
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.
[0050]
The focus vicinity determination circuit 505 evaluates these 20 focus direction data to determine whether or not the focus is near the 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.
[0051]
In the lens control amount calculation circuit 503, the movement direction and the movement amount of the lens are determined from the output of the focus direction determination circuit 502, the level of the focus signal VF, the result of the focus vicinity determination circuit 505, and the data of the focus vicinity data memory 506. And outputs a lens control amount to the lens driving unit 6.
[0052]
When it is not determined by the focus vicinity determination circuit 505 that the focus is near the focus, the data of the focus vicinity data memory 506 is not used, and the output of the focus direction determination circuit 502 and the level of the focus signal VF are used. To determine the direction and amount of movement of the lens. When the near focus determination circuit 505 determines that the focus is near the focus, the level of the focus near focus signal is the largest by looking at the data in the near focus data memory 506 during the near focus period. The lens position when taking the value is regarded as the in-focus position, and when the lens is stopped, the moving direction and the moving amount of the lens are determined using the near-focus lens control amount associated with the maximum value of the near-focus focal signal. decide.
[0053]
With these configurations and operations, the moving amount of the lens is adaptively changed according to whether or not the lens is near the focus, and when the lens is stopped, the maximum value of the past focus signal levels during the near-focus period is set. The focus is automatically adjusted by moving and stopping the lens using the lens control amount to be taken.
[0054]
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 further detail. 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,
VF ≧ LEV2
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
And MV4 is, for example, a minimum unit amount.
[0055]
Next, the relationship between the focus signal VF and the lens movement will be described with reference to FIG.
[0056]
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.
[0057]
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. 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.
[0058]
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. 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.
[0059]
As described above, since the movement of the lens in the vicinity of the in-focus state can be minimized irrespective of the photographing conditions of the subject, the disturbance of the image due to hunting can be suppressed as much as possible.
[0060]
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.
[0061]
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.
[0062]
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. It is assumed that the wobbling amplitude amount is added to the lens movement amount and output to the lens driving unit 6 as a lens control amount.
[0063]
Next, the relationship between the timing at which the lens is stopped, the responsiveness, and the focusing accuracy (lens stop variation) will be described.
[0064]
The step interval of the near-focus lens control amount stored in the near-focus data memory depends on the movement amount of the lens at that time. Therefore, in the case where the near focus determination circuit 505 stops the lens immediately after determining that it is near the focus, the response is good, but the stop precision of the lens is such that the near focus lens control amount is other than the movement amount MV4. The step interval is defined by the movement amount.
[0065]
On the other hand, it is determined that the lens is in the vicinity of the in-focus state, the lens movement amount is reduced to MV4, and then the lens is stopped after a predetermined time (for example, 20 fields). And the stop control can be performed with high accuracy.
[0066]
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.
[0067]
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.
[0068]
Then, the lens control amount calculation circuit 503 sets the timing (Z2 in FIG. 3) after 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 to be stopped regardless of the lens position of the focusing lens 1a. When the lens is stopped, the lens position when the level of the near focus signal stored in the near focus data memory 506 takes the largest value (when the lens passes through the focus position) is regarded as the focus position. By using the near-focus lens control amount associated with the maximum value of the near-focus focus signal, the moving direction and the moving amount of the lens are determined, and the lens can be finally stopped at the in-focus position.
[0069]
With the above-described configuration and operation, by performing the near focus determination and using the data in the vicinity of focus at the time of stop to stop the camera, the responsiveness is improved in places other than near the focus, and Thus, the quality and accuracy can be improved.
[0070]
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.
[0071]
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 is increased, even when the wobbling is performed over the in-focus position and the cycle of the direction determination is increased, the in-focus vicinity determination is performed stably and accurately. Therefore, there is also an advantage that the movement amount MV2 and the movement amount MV3 can be made larger and the responsiveness is improved.
[0072]
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.
[0073]
In addition, during the period when the level of the focus signal VF is not higher than the predetermined value, it is determined that the focus direction data is unreliable due to the influence of noise, and the result of the focus proximity determination is invalidated. By stopping and not always in the vicinity of focus, accurate near focus determination can be performed.
[0074]
The lens control amount stored in the near focus data memory 506 does not need to be the data itself output to the lens driving means, but a value (for example, a target position or a current position) corresponding to lens position information. Needless to say, the information may be stored and only needs to be converted into the lens control amount.
[0075]
Note that the lens driving unit 6 does not necessarily need to be a linear motor, but if a linear motor is used, high-speed driving can be performed. For example, hill-climbing control can be performed while wobbling is always performed. There is a feature that the focusing direction used for the determination can always be detected stably and accurately.
[0076]
Further, in the present embodiment, the response and the focusing accuracy are improved by performing the position feedback control by providing the lens position detection circuit, but for example, the open control may be performed by using the stepping motor. A similar effect can be obtained for improving the accuracy. In this case, since it is not necessary to provide a lens position detection circuit, the cost can be reduced.
[0077]
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.
[0078]
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.
[0079]
【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.
[0080]
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 showing a configuration of an automatic focusing device according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing an image of a hill-climbing operation by lens movement amount control in the embodiment; FIG. 4 is a block diagram showing a configuration of a conventional automatic focus adjustment device. FIG. 5 is a schematic diagram showing an operation image of the same focus signal detection. FIG. 6 is a schematic diagram showing an operation image of the same focus signal detection. FIG. 7 is a schematic view showing an image of a hill-climbing operation according to FIG. 7. FIG. 7 is a schematic view showing the lens behavior in the case of subject B in FIG.
Reference Signs List 1 photographing lens 1a focus adjusting lens 2 imaging means 3 video signal generation circuit 4 focus signal detection circuit 5 lens control circuit 502 focusing direction determination circuit 503 lens control amount calculation circuit 504 focusing direction memory 505 focusing proximity determination circuit 506 Near focus data memory 6 Lens drive unit

Claims (6)

A photographing lens including a focus adjusting lens, a lens driving unit that drives or stops the focus adjusting lens according to a lens control amount, and an imaging unit that photoelectrically converts a subject image formed through the photographing lens, A video signal generating means for performing predetermined signal processing on an output of the imaging means to generate a video signal; and a focus indicating a degree of contrast of a subject at predetermined time intervals by extracting a predetermined frequency band from the video signal. A focus signal detecting means for detecting a signal; a focus direction determining means for determining a focus direction based on an increase or a decrease in a time-varying component of the focus signal and outputting a focus direction signal indicating a far side or a near side; A focusing direction storing means for storing a plurality of direction signals; a focusing proximity determining means for determining whether or not the plurality of focusing direction signals are in the vicinity of focusing; and a focusing proximity determining means. Impatience Near-focus data storage means for storing the focus signal and the lens control amount during the period in which it is determined that the focus signal is near focus and the near-focus lens control amount, and the focus signal and the near focus. A lens control amount calculating unit that determines a moving direction and a moving amount of the focus adjusting lens based on the determination result of the determining unit, the in-focus near focus signal, and the in-focus near lens control amount, and outputs as the lens control amount; With
The lens control amount calculating means, after a lapse of a predetermined time after the in-focus vicinity determining means has determined that the in-focus state is near, the in-focus near focus signal stored in the in-focus near data storage means and the in-focus near lens An automatic focus adjustment device, wherein a focus adjustment lens is stopped based on a control amount. When the focusing lens is stopped, a lens control amount calculating means for outputting, as a lens control amount, a near-focus lens control amount at which the near-focus focus signal is maximized. Item 6. The automatic focusing device according to Item 1. A lens control amount calculating means, wherein the lens movement amount is made smaller during the period in which the focus vicinity determination means determines that the focus is in the vicinity of the focus as compared to outside the period. Item 3. The automatic focusing device according to any one of Items 1 to 2. 3. A lens control amount calculating means, wherein the lens control amount calculating means outputs a lens control amount for stopping the lens when the in-focus vicinity judging means judges that it is near the in-focus state. An automatic focusing device according to any of the preceding claims. During the period in which the in-focus vicinity determining means determines that the lens is near the in-focus state, the moving amount of the lens is made smaller than that in the out-of-period. 3. The automatic focus adjusting device according to claim 1, further comprising a lens control amount calculating unit that outputs a lens control amount for stopping the lens. 6. The apparatus according to claim 1, further comprising a focus vicinity determination unit that determines that the focus is near the focus only when the focus direction signal is equal to or more than a predetermined number of times on each of the far side and the near side. An automatic focusing device according to any of the preceding claims.

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