Patent Abstract:
A focus adjustment apparatus, which attains focus adjustment by extracting, as a focal point voltage, a predetermined frequency component of a video signal obtained from an image sensor upon sensing an image of an object, and moving a focus adjustment member in an optical axis direction using a moving unit to maximize the focal point voltage, has a detector that detects a half-stroke state of a shutter button, and a full-stroke state which is set via the half-stroke state, and a controller that executes focus adjustment control for the half-stroke state upon detection of the half-stroke state, and selectively enables or disables the focus adjustment control for the half-stroke state in accordance with a time elapsed from detection of the half-stroke state until detection of the full-stroke state, upon detection of the full-stroke state.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to an automatic focus adjustment apparatus and method used in various video cameras and the like. 
   BACKGROUND OF THE INVENTION 
   Auto-focus apparatuses for recent video cameras prevalently adopt a system which attains focus adjustment by detecting sharpness of a frame from a video signal obtained by photoelectrically converting an object image by an image sensing element or the like so as to obtain an AF (auto focus) evaluation value, and controlling a focus lens position so as to maximize the AF evaluation value. 
   As the AF evaluation value, a high-frequency component level of a video signal, which is extracted by a bandpass filter of a given frequency band, is generally used. That is, when a normal object image is sensed, the high-frequency component level increases as the focus lens position approaches an in-focus position. Hence, a point corresponding to the maximum high-frequency component level is determined as an in-focus position. 
   An actual video camera that can sense a still image executes AF control as follows. That is, the focus lens is controlled to smoothly maintain an in-focus position during monitoring before sensing a still image. When the user has pressed the release switch to sense a still image, the focus lens is controlled to quickly move to an in-focus position. 
   However, when the release switch for sensing a still image has half- and full-stroke positions, a blurred image may be recorded depending on the depression timing of the release switch by the user. In order to avoid such blurred image, the AF in-focus time is prolonged. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in consideration of the above situation, and has as its object to execute optimal lens control in response to a user&#39;s input especially in sensing a still image so as to prevent a blurred image from being captured. 
   According to the present invention, the foregoing object is attained by providing a focus adjustment apparatus, which attains focus adjustment by extracting, as a focal point voltage, a predetermined frequency component of a video signal obtained from an image sensor upon sensing an image of an object, and moving a focus adjustment member in an optical axis direction using a moving unit to maximize the focal point voltage, comprising: 
   a detector that detects two input states including a first input state, and a second input state which is set via the first input state; and 
   a controller that executes focus adjustment control for the first input state upon detection of the first input state, and selectively enables or disables the focus adjustment control for the first input state in accordance with a time elapsed from detection of the first input state until detection of the second input state, upon detection of the second input state. 
   According to the present invention, the foregoing object is also attained by providing a focus adjustment method, which attains focus adjustment by extracting, as a focal point voltage, a predetermined frequency component of a video signal obtained from an image sensor upon sensing an image of an object, and moving a focus adjustment member in an optical axis direction using a moving unit to maximize the focal point voltage, comprising: 
   monitoring a first input state of an input unit which can input two input states including the first input state, and a second input state which is set via the first input state; 
   executing focus adjustment control for the first input state upon detection of the first input state; 
   monitoring the second input state; and 
   selectively enabling or disabling the focus adjustment control for the first input state in accordance with a time elapsed from detection of the first input state until detection of the second input state, upon detection of the second input state. 
   Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a block diagram for explaining an example of an arrangement of a video camera according to an embodiment of the present invention; 
       FIG. 2  is a graph showing the relationship between the focus lens position and voltage level in automatic focus adjustment according to the embodiment of the present invention; 
       FIG. 3  is a flow chart associated with a main AF process in automatic focus adjustment according to the embodiment of the present invention; 
       FIG. 4  is a flow chart associated with a microstep drive operation in automatic focus adjustment according to the embodiment of the present invention; 
       FIG. 5  is a graph showing an elapsed time of the focus lens operation in automatic focus adjustment according to the embodiment of the present invention; 
       FIG. 6  is a flow chart associated with a hill-climbing operation in automatic focus adjustment according to the embodiment of the present invention; 
       FIG. 7  is a graph showing the relationship between the focus lens position and evaluation value in automatic focus adjustment according to the embodiment of the present invention; 
       FIG. 8  is a flow chart associated with a general AF operation in sensing a still image; 
       FIG. 9  is a flow chart associated with a still image AF process according to the embodiment of the present invention; and 
       FIG. 10  is a flow chart associated with an AF operation in sensing a still image according to the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of the present invention will now be described in detail in accordance with the accompanying drawings. 
   An example of the arrangement of a video camera which can sense a still image according to an embodiment of the present invention will be described first. Referring to  FIG. 1 , reference numeral  101  denotes a stationary first group lens;  102 , a zoom lens that attains zooming;  103 , an aperture;  104 , a stationary second group lens; and  105 , a focus compensation lens (to be referred to as a focus lens hereinafter) which has both a function of correcting movement of a focal plane upon zooming, and a focus adjustment function. Reference numeral  106  denotes an image sensing element such as a CCD or the like (to be referred to as a “CCD” hereinafter, but the present invention is not limited to the CCD); and  107 , a correlated double sampling/automatic gain controller (CDS/AGC) for sampling the output from the CCD  106  and adjusting its gain. Reference numeral  108  denotes a camera signal processing circuit for processing the output signal from the CDS/AGC  107  for a signal compatible to a still image recording device  109  (to be described below). Reference numeral  109  denotes a still image recording device which uses a semiconductor memory. 
   Reference numeral  110  denotes a lens motor as an actuator for moving the focus lens  105 ; and  111 , a lens driver for driving the motor  110  in accordance with a signal from an AF microcomputer  113  (to be described later). Reference numeral  112  denotes an AF evaluation value processing circuit for extracting a high-frequency component used in focus detection from the output signal of the CDS/AGC  107 ; and  113 , an AF microcomputer for controlling the driver  111  on the basis of the output signal from the AF evaluation value processing circuit  112  to drive the focus lens  105 , and switching AF control in accordance with an input from a still image release switch  114 . 
   Reference numeral  114  denotes the still image release switch, which can detect two states (half stroke, full stroke) in accordance with the degree of depression by the user. In this case, when the user presses the release switch  114 , the first state (to be referred to as a half-stroke state hereinafter) is detected first, and the second state (to be referred to as a full-stroke state hereinafter) is then detected. Reference numeral  115  denotes a monitor device which displays the output signal from the camera signal processing circuit  108 , and is used to monitor a sensed scene. 
   In the camera system with the arrangement shown in  FIG. 1 , the AF microcomputer  113  normally executes automatic focus adjustment by moving the focus lens  105  so as to maximize the output signal level of the AF evaluation value processing circuit  112 , in order to focus on a monitored image (see  FIG. 2 ). When the half-stroke state is detected upon depression of the release switch  114 , the AF microcomputer  113  executes an AF operation for still image sensing to search for an in-focus point, and controls the focus lens  105  to stop at the in-focus point. On the other hand, when the full-stroke state is detected, the AF microcomputer  113  stops the focus lens  105 , and issues a recording command to the still image recording device  109 . When the user wants to sense a still image of an object after focus adjustment, he or she need only wait for an in-focus state attained by the AF control while pressing the release switch  114  to its half-stroke position. On the other hand, when the user wants to sense a still image of an object immediately, he or she can press the release switch  114  to its full-stroke position. 
   The AF control which is done by the AF microcomputer  113  to monitor an image in this embodiment will be described in detail below with reference to  FIGS. 3 to 7 . 
     FIG. 3  explains the overall operation of the monitor AF process. Step S 301  indicates the start of the process. In step S 302 , a microstep drive operation is made to determine whether or not an in-focus point is reached, and to determine a direction in which an in-focus point is present if the in-focus point is not reached. A detailed operation in this step will be described later with reference to  FIG. 4 . 
   If it is determined in step S 303  that the in-focus position is reached in step S 302 , the flow advances to step S 309  to start an in-focus/re-drive determination process (to be described later). If the in-focus position is not reached in step S 302 , the flow advances to step S 304 . If it is determined in step S 304  that the direction is determined in step S 302 , the flow advances to step S 305  to perform hill-climbing drive control; otherwise, the flow returns to step S 302  to continue the microstep drive operation. In step S 305 , the focus lens undergoes high-speed hill-climbing drive control in a direction to increase the evaluation value. A detailed operation in this case will be described later with reference to  FIG. 6 . 
   If it is determined in step S 306  that the evaluation value has exceeded a peak in step S 305 , the flow advances to step S 307 ; otherwise, the flow returns to step S 305  to continue the hill-climbing drive operation. In step S 307 , the focus lens is returned to the focus lens position corresponding to the peak evaluation value during the hill-climbing drive operation. If it is determined in step S 308  that the focus lens is returned to the focus lens position corresponding to the peak evaluation value in step S 307 , the flow returns to step S 302  to execute the microstep drive operation again. If it is determined in step S 308  the focus lens is not returned to the focus lens position corresponding to the peak evaluation value in step S 307 , the flow returns to step S 307  to continue the operation for returning the lens to the peak position. 
   The in-focus/re-drive determination process which starts in step S 309  will be described below. In step S 309 , the AF evaluation value at the in-focus position fetched during the microstep drive operation in step S 302  is stored, as will be described later. In step S 310 , the latest AF evaluation value is fetched. In step S 311 , the AF evaluation value stored in step S 309  is compared with the latest AF evaluation value fetched in step S 310  to see if a variation of the AF evaluation value is large. If the AF evaluation value varies largely, it is determined that the focal point position has changed due to a change in object position, a change in object to be sensed, or the like. Hence, the flow returns to step S 302  to restart the microstep drive operation. If the AF evaluation value does not vary, the flow advances to step S 312 . In step S 312 , the focus lens  105  is stopped, and the flow returns to step S 310  to continue the in-focus/re-drive determination process. 
   The microstep drive operation will be described below with reference to  FIG. 4 . Step S 401  indicates the start of the process. In step S 402 , the AF evaluation value is fetched from the AF evaluation value processing circuit  112 . If it is determined in step S 403  that the evaluation value fetched in step S 402  is smaller than the previous evaluation value, the flow advances to step S 404 ; otherwise, the flow advances to step S 405 . In step S 404 , the focus lens  105  is driven by a predetermined amount in a direction opposite to the previous drive operation. On the other hand, in step S 405  the focus lens  105  is driven by a predetermined amount in the same direction as the previous drive operation. If it is determined in step S 406  that the same drive direction of the focus lens  105  is successively detected a predetermined number of times, the flow advances to step S 410 ; otherwise, the flow advances to step S 407 . 
   It is checked in step S 407  if reciprocal movement of the focus lens is repeated within a given area a predetermined number of times. If reciprocal movement is repeated, the flow advances to step S 409 ; otherwise, the flow advances to step S 408  to end the current process. In this case, in the aforementioned process shown in  FIG. 3 , since NO in step S 303  and YES in step S 304 , the flow advances to step S 305  to execute the hill-climbing drive operation. On the other hand, it is determined in step S 409  that an in-focus point is detected, and the process ends. In this case, in the aforementioned process shown in  FIG. 3 , since YES in step S 303 , the flow advances to step S 309  and subsequent steps to execute the in-focus/re-drive determination process. 
     FIG. 5  shows a lapse of time of the aforementioned focus lens operation. Evaluation value A corresponding to a change accumulated on the CCD during a period A is fetched at time T A , and evaluation value B corresponding to a charge accumulated on the CCD during a period B is fetched at time T B . At time T B , evaluation values A and B are compared. If A&lt;B, the focus lens  105  is driven in the same direction as the previous focus lens drive direction; if A&gt;B, the focus lens  105  is driven in the opposite direction. 
   The hill-climbing drive operation will be described below using  FIG. 6 . Step S 601  indicates the start of the process. In step S 602 , the AF evaluation value is fetched from the AF evaluation value processing circuit  112 . If it is determined in step S 603  that the evaluation value fetched in step S 602  is larger than the previous evaluation value, the flow advances to step S 604 ; otherwise, the flow advances to step S 606 . In step S 604 , the focus lens  105  is driven by a predetermined amount at a predetermined speed in the same direction as the previous drive operation, and the current process ends. The flow then advances to step S 306  in  FIG. 3 . In this case, since NO in step S 306 , the flow returns to step S 305  to repeat the process in  FIG. 6 . 
   On the other hand, if it is determined in step S 606  that the evaluation value is not decreased after a peak, the flow advances to step S 607 ; otherwise, the process ends, and the flow advances to step S 306  in  FIG. 3 . In this case, since YES in step S 306 , the flow advances to step S 307 . In step S 607 , the focus lens  105  is driven at a predetermined speed in a direction opposite to the previous drive operation, and the current process ends. Then, the flow advances to step S 306  in  FIG. 3 . In this case, since NO in step S 306 , the flow returns to step S 305  to repeat the process in  FIG. 6 . 
   The focus lens operation determined in step S 606  above will be described below with reference to  FIG. 7 . In this case, since the evaluation value is decreased at A after passing a peak (YES in step S 606 ), it is determined that an in-focus point is found, and the hill-climbing drive operation ends. After the focus lens  105  is returned to the peak position of the AF evaluation value in steps S 307  and S 308 , the flow returns to step S 302  to start the microstep drive operation. On the other hand, since the evaluation value is decreased at B without passing any peak (NO in step S 606 ), it is determined that the lens is driven in a wrong direction, and the drive direction is reversed, thus continuing the hill-climbing drive operation. 
   As described above, the focus lens  105  is moved while repeating in-focus/re-drive determination→microstep drive→hill-climbing drive microstep drive→in-focus/re-drive determination. The AF microcomputer  113  of the camera controls to always maximize the AF evaluation value, thereby maintaining an in-focus state of a monitor image. 
   On the other hand, according to an example of an AF operation in sensing a still image, the focus lens  105  is either stopped at that position or stopped at a peak position after a search for the in-focus position, in accordance with the operation state of the release switch  114  for sensing a still image. This general operation example will be described below with reference to  FIG. 8 . This process is also executed by the AF microcomputer  113 . Step S 801  indicates the start of the process. In step S 802 , the aforementioned monitor AF process is executed. 
   In step S 803 , the release switch  114  is monitored. If the release switch  114  has been pressed to its full-stroke position, the flow jumps to step S 808  and subsequent steps. In step S 808 , the focus lens  105  is stopped at the current position, thus ending the AF process. If the release switch  114  has not been pressed to its full-stroke position, the flow advances to step S 804 . It is checked in step S 804  if the release switch  114  has been pressed to its half-stroke position. If the release switch  114  has been pressed to its half-stroke position, the flow advances to step S 805 . It is checked in step S 805  if a predetermined period of time has elapsed at the half-stroke position (whether the user really wants to hold the release switch at its half-stroke position or the half-stroke state is detected on the way to the full-stroke position). If the predetermined period of time has elapsed, the flow advances to step S 806  to execute a still image AF process. On the other hand, if the release switch has not been pressed to its half-stroke position or the predetermined period of time has not elapsed, the flow returns to step S 802  to continue the monitor AF process. It is checked in step S 807  if an in-focus point is detected in the still image AF process. If an in-focus point is detected, the flow advances to step S 808  to stop the AF control, thus ending the process. 
   The process in  FIG. 9  explains the still image AF process in step S 806  in  FIG. 8 . Step S 901  indicates the start of the process. It is determined in step S 902  whether or not the focus lens  105  is at a stop. If it is determined in step S 902  that the focus lens  105  is at a stop, the flow advances to step S 903 . In step S 903 , the focus lens begins to be driven toward the closest distance side, thus ending the current process. 
   If it is determined in step S 902  that the focus lens is moving, the flow advances to step S 905  to check if the focus lens  105  is moving toward the closest distance side. If it is determined in step S 905  that the focus lens  105  is moving toward the closest distance side, the flow advances to step S 906 . In step S 906 , the AF evaluation value is monitored. If the AF evaluation value is decreased, the flow advances to step S 907 . In step S 907 , the focus lens begins to be driven toward the infinity side, thus ending the current process. If it is determined in step S 906  that the AF evaluation value is not decreased, the current process directly ends. 
   If it is determined in step S 905  that the focus lens  105  is moving toward the infinity side, the flow advances to step S 908 . In step S 908 , a change in AF evaluation value is monitored. If the AF evaluation value has exceeded a peak, the flow advances to step S 909 . In step S 909 , the focus lens is moved to and stopped at a focus lens position at which the peak of the AF evaluation value is detected in step S 908 , thus ending the still image AF process. If it is determined in step S 908  that the AF evaluation value has not exceeded a peak, the current process ends. In this way, the peak of the AF evaluation value can be detected at high speed. 
   As described above, during monitoring before sensing an image, the focus lens is controlled to smoothly maintain an in-focus state. Upon depression of the release switch  114 , the focus lens  105  is controlled to reach an in-focus position at high speed, thereby AF control operations suited to individual situations are executed. 
   The full-stroke state of the release switch  114  for sensing a still image is detected only after the half-stroke state. For this reason, if an AF search operation starts immediately after detection of the half-stroke state, a blurred image is recorded if the release switch  114  is immediately pressed to its full-stroke position. To solve this problem, the control may wait for a predetermined period of time after detection of the half-stroke state, and the AF search operation may start after it is confirmed that the release switch is not pressed to its full-stroke position. However, with this control, since the AF search operation cannot start immediately after detection of the half-stroke state, the AF in-focus time is prolonged. 
   The control of the camera AF microcomputer according to the present invention will be described in detail below using  FIG. 10 . This process is executed by the AF microcomputer  113 . Step S 1001  indicates the start of the process. Step S 1002  corresponds to the aforementioned monitor AF process. In step S 1003 , the release switch  114  is monitored. If the release switch  114  has not been pressed to its half-stroke position, the flow returns to step S 1002  to continue to the monitor AF process. If the release switch  114  has been pressed to its half-stroke position, the flow advances to step S 1004 . In step S 1004 , the current focus lens position is stored in a memory in the AF microcomputer  113 . 
   In step S 1005 , the aforementioned still image AF process is executed. It is checked in step S 1006  if the release switch has been pressed to its full-stroke position. If the release switch has not been pressed to its full-stroke position, the flow advances to step S 1007 . It is checked in step S 1007  if an in-focus point is detected. If an in-focus point is not detected, the flow returns to step S 1005  to continue the still image AF process. If an in-focus point is detected, the flow advances to step S 1008  to stop the AF process. 
   If it is determined in step S 1006  that the release switch has been pressed to its full-stroke position, the flow advances to step S 1010  to determine whether or not a predetermined period of time has elapsed after detection of the half-stroke state. This predetermined period of time is experimentally determined based on time periods detected as the half-stroke state upon depressing the release button to its full-stroke position. If the predetermined period of time has not elapsed yet, it is determined that the user originally wants to press the release switch to its full-stroke position, and the focus lens  105  is returned to the focus lens position stored in the microcomputer  113 , since the focus lens position at the beginning of depression of the release switch  114  is optimal. On the other hand, if the release switch  114  has been pressed to its full-stroke position after an elapse of the predetermined period of time or more, it is determined that the user wants to capture the current image, and the focus lens  105  is stopped at the current focus lens position. 
   In this way, since the AF search operation can start immediately after detection of the half-stroke state in accordance with the release switch  114  for sensing a still image, the AF in-focus time can be shortened. When the full-stroke state is detected within a predetermined period of time after detection of the half-stroke state, it is determined that the user originally wants to press the release switch to its full-stroke position, and the focus lens  105  is returned to the focus lens position saved at the beginning of the AF process. In this way, the AF search operation can be prevented from being erroneously started in response to detection of the half-stroke state on the ways to the full-stroke position and, hence, a blurred image can be prevented from being captured during the search operation. Hence, an appropriate image can be recorded, and the image sensing time can be effectively shortened. 
   The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore to apprise the public of the scope of the present invention, the following claims are made.

Technology Classification (CPC): 7