Patent Document

FIELD OF THE INVENTION 
   The present invention relates to an image sensing apparatus for various video cameras and, more particularly, to an autofocus adjustment technique in photographing a still picture. 
   BACKGROUND OF THE INVENTION 
   In AF (AutoFocus) devices for recent video cameras, the following focus adjustment method is a mainstream. That is, the sharpness of a frame is detected from a video signal obtained by photoelectrically converting an object image by an image sensing element or the like. The sharpness is set as an AF evaluation value, and movement of a focus lens is so controlled as to maximize the AF evaluation value. 
   In general, the AF evaluation value is the voltage level of the high-frequency component of a video signal extracted by a bandpass filter having a given band. When a normal object image is photographed, the voltage level (focus voltage level) of the high-frequency component of the video signal increases its voltage level value as the image is set in an in-focus state, as shown in  FIG. 2 . A point where the voltage level value maximizes is an in-focus position. 
   The hardware arrangement of an actual video camera will be described in detail with reference to  FIG. 1 . 
   In  FIG. 1 , reference numeral  101  denotes a fixed first lens group;  102 , a zoom lens which performs zooming;  103 , a stop;  104 , a fixed second lens group; and  105 , a focus compensation lens (to be referred to as a focus lens hereinafter) having a function of correcting movement of a focal plane along with zooming operation and a focusing function. 
   Reference numeral  106  denotes an image sensing element (CCD);  107 , an AGC which amplifies an output from the CCD  106 ; and  108 , a camera signal processing circuit which converts output signals from the AGC  107  into signals corresponding to a moving picture recording device  109  and still picture recording device  116  (to be described below). The moving picture recording device  109  uses a magnetic tape as a recording medium, and the still picture recording device  116  uses a semiconductor memory as a recording medium. 
   Reference numerals  110  and  112  denote motors for moving the zoom lens  102  and focus lens  105 ;  111  and  113 , drivers which drive the motors  110  and  112  in accordance with signals from a camera AF microcomputer  115  (to be described below); and  114 , an AF evaluation value processing circuit which extracts, from an output signal from the CCD  106 , a high-frequency component and luminance difference component (difference between the maximum and minimum values of the luminance level of a video signal) used to perform focus detection. 
   The AF microcomputer  115  controls the motors  110  and  112  via the drivers  111  and  113  on the basis of output signals from the AF evaluation value processing circuit  114 . The AF microcomputer  115  also performs various types of control such that the recording destination of an output signal from the camera signal processing circuit  108  is switched to the moving picture recording device  109  or still picture recording device  116  in accordance with ON operations of a moving picture trigger switch  117  and still picture release switch  118 . 
   The AF microcomputer  115  comprises a CPU  115   a , ROM  115   b , and RAM  115   c . The CPU  115   a  executes various processes on the basis of control programs (including control programs corresponding to flow charts (to be described later)) stored in the ROM  115   b . At this time, the CPU  115   a  uses the RAM  115   c  as a work area or the like. 
   In the camera system having the arrangement shown in  FIG. 1 , the AF microcomputer  115  automatically adjusts the focus by moving the focus lens  105  so as to maximize the output signal level of the AF evaluation value processing circuit  114 . The AF microcomputer  115  issues a recording instruction to the moving picture recording device  109  upon reception of a moving picture trigger signal upon ON operation of the moving picture trigger switch  117 . The AF microcomputer  115  issues a recording instruction to the still picture recording device  116  upon reception of a release signal upon ON operation of the still picture release switch  118 . 
   AF control by the AF microcomputer  115  in photographing a moving picture will be explained in detail with reference to  FIGS. 3 to 7 . 
   After moving picture AF processing starts (step S 301 ), the CPU  115   a  of the AF microcomputer  115  finely drives the focus lens  105  (step S 302 ). Fine driving processing will be described in detail later with reference to  FIG. 4 . Then, the CPU  115   a  checks whether the focus lens  105  is in focus by fine driving (step S 303 ). If NO in step S 303 , the CPU  115   a  checks whether the in-focus direction is determined by fine driving (step S 304 ). 
   If NO in step S 304 , the CPU  115   a  returns to step S 302 . If YES in step S 304 , the CPU  115   a  advances to step S 305 , and performs so-called hill-climbing driving of moving the focus lens  105  at a high speed in a direction in which the AF evaluation value increases. Hill-climbing driving processing will be described in detail later with reference to  FIG. 6 . The CPU  115   a  checks whether the AF evaluation value exceeds its peak by hill-climbing driving (step S 306 ). If NO in step S 306 , the CPU  115   a  returns to step S 305 , and continues hill-climbing driving. 
   If YES in step S 306 , the CPU  115   a  drives the focus lens  105  in an opposite direction in order to return the AF evaluation value to its peak during hill-climbing driving (step S 307 ). Then, the CPU  115   a  checks whether the AF evaluation value reaches its peak (step S 308 ). If NO in step S 308 , the CPU  115   a  returns to step S 307 , and continues the operation of returning the AF evaluation value to its peak. If YES in step S 308 , the CPU  115   a  returns to step S 302 , finely drives the focus lens  105 , and searches for the in-focus position of the next moving picture. 
   If YES in step S 303 , the CPU  115   a  stores an AF evaluation value for an in-focus state in the RAM  115   c  (step S 309 ), and performs reactivation determination processing for moving picture AF operation (step S 310 ). In reactivation determination processing, the CPU  115   a  compares the current AF evaluation value stored in step S 309  with the previous AF evaluation value, and if the values are different by a predetermined level or more, the CPU  115   a  determines that the focus lens  105  must be reactivated. 
   The CPU  115   a  checks whether the focus lens  105  is determined to be reactivated in reactivation determination processing (step S 311 ). If YES in step S 311 , the CPU  115   a  returns to step S 302 , and restarts fine driving operation in order to execute AF processing for the next moving picture. If NO in step S 311 , the CPU  115   a  stops the focus lens  105  (step S 312 ). The CPU  115   a  returns to step S 310  in order to perform AF control for subsequent moving pictures, and continues reactivation determination processing. 
   Details of fine driving processing in step S 302  of  FIG. 3  will be explained with reference to the flow chart of  FIG. 4 , and  FIG. 5 . 
   After fine driving processing starts (step S 401 ), the CPU  115   a  receives an AF evaluation value from the AF evaluation value processing circuit  114  (step S 402 ). The CPU  115   a  checks whether the current AF evaluation value received in step S 402  is larger than the previous AF evaluation value (step S 403 ). 
   If NO in step S 403 , the CPU  115   a  advances to step S 404 , and moves the focus lens  105  by a predetermined amount in an opposite direction. If YES in step S 403 , the CPU  115   a  advances to step S 405 , and moves the focus lens  105  by a predetermined amount in the current direction (forward/backward direction). 
   After the process in step S 404  or S 405 , the CPU  115   a  checks whether the direction determined as an in-focus direction is kept unchanged successively a predetermined number of times or more, i.e., whether the focus lens  105  moves in the same direction successively a predetermined number of times or more (step S 406 ). 
   If YES in step S 406 , the CPU  115   a  sets that the moving direction of the focus lens  105  for an in-focus state can be determined (step S 407 ), and ends fine driving processing. When fine driving processing ends through this route, hill-climbing driving in step S 305  of  FIG. 3  is executed. 
   If NO in step S 406 , the CPU  115   a  checks whether the focus lens  105  repeats direction reversal a predetermined number of times or more in almost the same area (step S 408 ). If NO in step S 408 , this means that the focus lens  105  has not reached the vicinity of an in-focus position. The CPU  115   a  returns to step S 402 , and continues fine driving processing. 
   If YES in step S 408 , this means that the focus lens  105  has reached the vicinity of an in-focus position (step S 409 ), and the CPU  115   a  ends fine driving processing. When fine driving processing ends through this route, the reactivation determination routine in step S 310  of  FIG. 3  is executed. 
   The processes in steps S 403  to S 405  will be described with reference to  FIG. 5 . 
   In  FIG. 5 , the CPU  115   a  receives at a timing T A  an AF evaluation value A for charges (image signal) accumulated in the CCD  106  during a period A, and receives at a timing T B  an AF evaluation value B for an image signal accumulated in the CCD  106  during a period B. At the timing T B , the CPU  115   a  compares the AF evaluation values A and B, if A&lt;B holds, keeps moving the focus lens  105  in the forward direction (current direction), and if A&gt;B holds, moves the focus lens  105  in an opposite direction. 
   Details of hill-climbing driving processing in step S 305  of  FIG. 3  will be explained with reference to the flow chart of  FIG. 6 , and  FIG. 7 . 
   After hill-climbing processing starts (step S 601 ), the CPU  115   a  receives an AF evaluation value from the AF evaluation value processing circuit  114  (step S 602 ). The CPU  115   a  checks whether the current AF evaluation value received in step S 602  is larger than the previous AF evaluation value (step S 603 ). 
   If YES in step S 603 , the CPU  115   a  drives the focus lens  105  in the forward direction at a predetermined speed (step S 604 ), and returns to step S 602 . 
   If NO in step S 603 , the CPU  115   a  checks whether the AF evaluation value exceeds its peak (step S 605 ). If the AF evaluation value does not exceed its peak, i.e., the current AF evaluation value becomes equal to or smaller than the previous AF evaluation value though the AF evaluation value does not exceed its peak, the AF microcomputer  115  determines that the direction is not correct, drives the focus lens  105  in an opposite direction at a predetermined speed (step S 606 ), and returns to step S 602 . 
   If the AF evaluation value exceeds its peak, i.e., the current AF evaluation value becomes equal to or smaller than the previous AF evaluation value as a result of exceeding the peak of the AF evaluation value, the CPU  115   a  determines that an in-focus point exists, and ends hill-climbing driving processing (step S 607 ). When hill-climbing processing ends in this manner, fine driving processing is executed in step S 302  of  FIG. 3 . 
   The significance of the processes in steps S 605  to S 607  of  FIG. 6  will be supplemented with reference to  FIG. 7 . 
   In  FIG. 7 , the upper MA decreases the AF evaluation value over the peak. The CPU  115   a  determines that an in-focus point exists and the focus lens  105  has passed through the in-focus point. Thus, the CPU  115   a  ends hill-climbing operation, and shifts to fine driving processing. The lower MB decreases the AF evaluation value without any peak. The CPU  115   a  determines that the moving direction of the focus lens  105  is not correct, reverses the moving direction, and continues hill-climbing operation. 
   As described above, the camera AF microcomputer  115  always maximizes the AF evaluation value by controlling movement of the focus lens  105  while repeating reactivation determination→fine driving→hill-climbing driving→fine driving→reactivation determination. 
   Japanese Patent Laid-Open No. 07-298120 proposes a method of normalizing an AF evaluation value by a luminance difference component and determining an in-focus degree. This method exploits the fact that the ratio of the luminance difference component and a high-frequency component serving as an AF evaluation value is constant at an in-focus point. If the ratio is a predetermined value or more, the focus lens is close to an in-focus point. If the ratio is very low, the focus lens is greatly in an out-of-focus state. In other words, an in-focus state can be determined to a certain extent from the ratio of the maximum value of the luminance difference component and the AF evaluation value. The determination result is used to tune the amplitude in fine driving (vibrations or reciprocation) or the speed in hill-climbing driving. 
   In recent years, video cameras having a still picture photographing mode have been implemented. In AF processing in photographing a still picture by this video camera, the focus lens  105  is moved in accordance with release operation for still picture photography to a lens position corresponding to the maximum AF evaluation value which has already been obtained by moving picture AF processing. Alternatively, in-focus control is performed again. 
   The former conventional AF processing in still picture photography will be explained with reference to the flow chart of  FIG. 16 . 
   After AF processing starts (step S 1601 ), the CPU  115   a  of the AF microcomputer  115  executes AF processing in moving picture photography that has been described with reference to  FIGS. 3 to 7  (step S 1602 ). The CPU  115   a  checks whether the still picture release switch  118  has been turned on to input a still picture release signal (step S 1603 ). If NO in step S 1603 , the CPU  115   a  returns to step S 1602 , and continues AF processing in moving picture photography. 
   If YES in step S 1603 , the CPU  115   a  moves the focus lens  105  to a position corresponding to the maximum AF evaluation value obtained by the preceding AF processing in moving picture photography (step S 1604 ). The CPU  115   a  records a still picture by controlling the camera signal processing circuit  108  and still picture recording device  116  (step S 1605 ), and ends AF processing in still picture photography (step S 1606 ). 
   The latter conventional AF processing in still picture photography will be described with reference to the flow chart of  FIG. 17 . 
   After AF processing starts (step S 1701 ), the CPU  115   a  of the AF microcomputer  115  executes AF processing in moving picture photography that has been described with reference to  FIGS. 3 to 7  (step S 1702 ). The CPU  115   a  checks whether the still picture release switch  118  has been turned on to input a still picture release signal (step S 1703 ). If NO in step S 1703 , the CPU  115   a  returns to step S 1702 , and continues AF processing in moving picture photography. 
   If YES in step S 1703 , the CPU  115   a  moves the focus lens  105  to the closest focusing (wide-angle) direction at a high speed (step S 1704 ), and checks whether the AF evaluation value decreases (step S 1705 ). If NO in step S 1705 , the CPU  115   a  returns to step S 1704 , and continues lens moving processing to the closest focusing direction. 
   If YES in step S 1705 , the CPU  115   a  moves the focus lens  105  to the infinity (telephoto) direction at a high speed (step S 1706 ). The CPU  115   a  monitors changes in AF evaluation value, and checks whether the AF evaluation value exceeds its peak (step S 1707 ). If NO in step S 1707 , the CPU  115   a  returns to step S 1706 , and continues lens moving processing to the infinity direction. 
   If YES in step S 1707 , the CPU  115   a  moves the focus lens  105  to the peak position (in-focus position) (step S 1708 ). The CPU  115   a  performs fine driving in  FIG. 4  to search for an accurate peak position (step S 1709 ). Fine driving processing is done in consideration of a case in which an actual in-focus position includes an error even if a peak position is detected during high-speed driving, or a case in which an object to be photographed moves. 
   The CPU  115   a  checks whether a peak position has been detected by fine driving processing of step S 1709  (step S 1710 ). If NO in step S 1710 , the CPU  115   a  returns to step S 1709 , and repeats fine driving processing. 
   If YES in step S 1710 , the CPU  115   a  moves the focus lens  105  to the peak position (step S 1711 ). The CPU  115   a  records a still picture by controlling the camera signal processing circuit  108  and still picture recording device  116  (step S 1712 ), and ends AF processing in still picture photography (step S 1713 ). 
   This prior art suffers the following problems. The moving time is short when the focus lens  105  is moved in accordance with release operation for still picture photography to a lens position corresponding to the maximum AF evaluation value obtained by the preceding moving picture AF processing. If the lens position corresponding to the maximum AF evaluation value obtained by moving picture AF processing is not an in-focus position, a blurred still picture is captured. 
   When in-focus control is newly executed though the lens position corresponding to the maximum AF evaluation value obtained by moving picture AF processing is an in-focus position, a predetermined time is necessarily required till reception of an image, undesirably generating a shutter time lag. 
   SUMMARY OF THE INVENTION 
   The present invention has been made to overcome the conventional drawbacks, and has as its object to improve the autofocus performance in photographing a still picture. 
   To solve the above-described problems and achieve the above object, an apparatus according to the first aspect of the present invention has the following arrangement. 
   That is, the apparatus comprises (A) a designating device which designates still picture photography, (B) a determining device which determines a focus adjustment state by a focus adjusting device when the designating device is operated, and (C) a control device which causes the focus adjusting device to perform at least two operations in accordance with the focus adjustment state determined by the determining device. 
   An apparatus according to the second aspect of the present invention has the following arrangement. 
   That is, the apparatus comprises (A) a designating device which designates still picture photography, (B) a determining device which determines a focus adjustment state by a focus adjusting device when the designating device is operated, and (C) a deciding device which decides, in accordance with the focus adjustment state determined by the determining device, whether first focus adjustment operation performed by the focus adjusting device before the designating device is operated is used for still picture photography, or second focus adjustment operation different from the first focus adjustment operation performed by the focus adjusting device after the designating device is operated is used for still picture photography. 
   An apparatus according to the third aspect of the present invention has the following arrangement. 
   That is, the apparatus comprises (A) a designating device which designates still picture photography, (B) a determining device which determines a focus adjustment state by a focus adjusting device when the designating device is operated, and (C) a deciding device which decides, in accordance with the focus adjustment state determined by the determining device, whether first focus adjustment operation performed by the focus adjusting device before the designating device is operated is used for still picture photography, or second focus adjustment operation newly performed independently of the first focus adjustment operation by the focus adjusting device after the designating device is operated is used for still picture photography. 
   A focus adjustment method according to the first aspect of the present invention has the following step. 
   That is, the focus adjustment method comprises the steps of determining a focus adjustment state by a focus adjusting device when an operation of designating still picture photography is done, and causing the focus adjusting device to perform at least two operations in accordance with the determined focus adjustment state. 
   A focus adjustment method according to the second aspect of the present invention has the following step. 
   That is, the focus adjustment method comprises the steps of determining a focus adjustment state by a focus adjusting device when an operation of designating still picture photography is done, and deciding, in accordance with the determined focus adjustment state, whether first focus adjustment operation performed by the focus adjusting device before the designating operation is done is used for still picture photography, or second focus adjustment operation different from the first focus adjustment operation performed by the focus adjusting device after the designating operation is done is used for still picture photography. 
   A focus adjustment method according to the third aspect of the present invention has the following step. 
   That is, the focus adjustment method comprises the steps of determining a focus adjustment state by a focus adjusting device when an operation of designating still picture photography is done, and deciding, in accordance with the determined focus adjustment state, whether first focus adjustment operation performed by the focus adjusting device before the designating operation is done is used for still picture photography, or second focus adjustment operation newly performed independently of the first focus adjustment operation by the focus adjusting device after the designating operation is done is used for still picture photography. 
   A focus adjustment computer control program according to the first aspect of the present invention has the following program codes. 
   That is, the focus adjustment computer control program comprises program codes of determining a focus adjustment state by a focus adjusting device when an operation of designating still picture photography is done, and causing the focus adjusting device to perform at least two operations in accordance with the determined focus adjustment state. 
   A focus adjustment computer control program according to the second aspect of the present invention has the following program codes. 
   That is, the focus adjustment computer control program comprises program codes of determining a focus adjustment state by a focus adjusting device when an operation of designating still picture photography is done, and deciding, in accordance with the determined focus adjustment state, whether first focus adjustment operation performed by the focus adjusting device before the designating operation is done is used for still picture photography, or second focus adjustment operation different from the first focus adjustment operation performed by the focus adjusting device after the designating operation is done is used for still picture photography. 
   A focus adjustment computer control program according to the third aspect of the present invention has the following program codes. 
   That is, the focus adjustment computer control program comprises program codes of determining a focus adjustment state by a focus adjusting device when an operation of designating still picture photography is done, and deciding, in accordance with the determined focus adjustment state, whether first focus adjustment operation performed by the focus adjusting device before the designating operation is done is used for still picture photography, or second focus adjustment operation newly performed independently of the first focus adjustment operation by the focus adjusting device after the designating operation is done is used for still picture photography. 
   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 
       FIG. 1  is a block diagram showing the hardware arrangement of a video camera to which the present invention is applied; 
       FIG. 2  is a graph for explaining an AF evaluation value; 
       FIG. 3  is a flow chart schematically showing AF processing in moving picture photography; 
       FIG. 4  is a flow chart showing fine driving processing of a focus lens in AF processing; 
       FIG. 5  is a graph for explaining the moving direction of the focus lens in fine driving processing; 
       FIG. 6  is a flow chart showing hill-climbing processing in AF processing; 
       FIG. 7  is a graph for explaining the moving direction of the focus lens in hill-climbing processing; 
       FIG. 8  is a flow chart showing AF processing in still picture photography according to the first embodiment of the present invention; 
       FIG. 9  is a flow chart subsequent to  FIG. 8 ; 
       FIG. 10  is a flow chart showing AF processing in still picture photography according to the second embodiment of the present invention; 
       FIG. 11  is a flow chart subsequent to  FIG. 10 ; 
       FIG. 12  is a flow chart showing AF processing in still picture photography according to the third embodiment of the present invention; 
       FIG. 13  is a flow chart subsequent to  FIG. 12 ; 
       FIG. 14  is a flow chart showing AF processing in still picture photography according to the fourth embodiment of the present invention; 
       FIG. 15  is a flow chart subsequent to  FIG. 14 ; 
       FIG. 16  is a flow chart showing conventional AF processing in still picture photography; and 
       FIG. 17  is a flow chart showing another conventional AF processing in still picture photography. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The following embodiments are applied to a video camera having a still picture photographing mode. The hardware arrangement of the video camera is the same as that shown in  FIG. 1 , and a description thereof will be omitted. 
   First Embodiment 
   AF processing in still picture photography according to the first embodiment will be described with reference to the flow charts of  FIGS. 8 and 9 . 
   After AF processing starts (step S 801 ), a CPU  115   a  of an AF microcomputer  115  performs AF processing in moving picture photography described with reference to  FIGS. 3 to 7  (step S 802 ). The CPU  115   a  checks whether a still picture release switch  118  has been turned on to input a still picture release signal (step S 803 ). If NO in step S 803 , the CPU  115   a  returns to step S 802 , and continues AF processing in moving picture photography. 
   If YES in step S 803 , the CPU  115   a  checks whether a focus lens  105  stays in almost the same area for a predetermined time or longer in AF processing in moving picture photography, in other words, whether the focus lens  105  repeats direction reversal a predetermined number of times or more in almost the same area (step S 804 ). 
   If YES in step S 804 , this means that an in-focus position has been detected by the preceding AF processing in moving picture photography. The CPU  115   a  moves the focus lens  105  to a position corresponding to the maximum AF evaluation value obtained by the preceding AF processing in moving picture photography (step S 805 ). The CPU  115   a  records a still picture by controlling a camera signal processing circuit  108  and still picture recording device  116  (step S 806 ), and ends AF processing in still picture photography (step S 807 ). 
   If NO in step S 804 , this means that any in-focus position has not been detected yet by the preceding AF processing in moving picture photography. The CPU  115   a  moves the focus lens  105  to the closest focusing (wide-angle) direction at a high speed (step S 808 ), and checks whether the AF evaluation value decreases (step S 809 ). If NO in step S 809 , the CPU  115   a  returns to step S 808 , and continues lens moving processing to the closest focusing direction. 
   If YES in step S 809 , the CPU  115   a  moves the focus lens  105  to the infinity (telephoto) direction at a high speed (step S 810 ). The CPU  115   a  monitors changes in AF evaluation value, and checks whether the AF evaluation value exceeds its peak (step S 811 ). If NO in step S 811 , the CPU  115   a  returns to step S 810 , and continues lens moving processing to the infinity direction. 
   If YES in step S 811 , the CPU  115   a  moves the focus lens  105  to the peak position (in-focus position) (step S 812 ). The CPU  115   a  performs fine driving in  FIG. 4  to search for a peak position (step S 813 ). 
   Fine driving processing is done in consideration of a case in which an actual in-focus position includes an error even if a peak position is detected during high-speed driving, or a case in which an object to be photographed moves. 
   Then, the CPU  115   a  checks whether the focus lens  105  repeats direction reversal a predetermined number of times or more in almost the same area in fine driving processing of step S 813  (step S 814 ). If NO in step S 814 , this means that any in-focus position has not been detected yet by fine driving processing of step S 813 . The CPU  115   a  returns to step S 813 , and continues fine driving processing. 
   If YES in step S 814 , this means that an in-focus position has been detected by fine driving processing of step S 813 . The CPU  115   a  moves the focus lens  105  to a lens position corresponding to the maximum AF evaluation value obtained by fine driving processing (step S 815 ). The CPU  115   a  records a still picture by controlling the camera signal processing circuit  108  and still picture recording device  116  (step S 816 ), and ends AF processing in still picture photography (step S 817 ). 
   In the first embodiment, when an in-focus position is considered to be detected by the preceding moving picture AF processing upon reception of a still picture photographing/recording instruction, the focus lens  105  is quickly moved to the in-focus position, AF processing is stopped, and a still picture is recorded. The first embodiment can, therefore, realize photography free from any shutter time lag. 
   If an in-focus position is considered not to be detected by the preceding moving picture AF processing upon reception of a still picture photographing/recording instruction, an in-focus position is immediately detected, the focus lens  105  is moved to the in-focus position, AF processing is stopped, and a still picture is recorded, thereby preventing recording any blurred still picture. 
   Second Embodiment 
   AF processing in still picture photography according to the second embodiment will be described with reference to the flow charts of  FIGS. 10 and 11 . 
   After AF processing starts (step S 1001 ), a CPU  115   a  of an AF microcomputer  115  performs AF processing in moving picture photography described with reference to  FIGS. 3 to 7  (step S 1002 ). The CPU  115   a  checks whether a still picture release switch  118  has been turned on to input a still picture release signal (step S 1003 ). If NO in step S 1003 , the CPU  115   a  returns to step S 1002 , and continues AF processing in moving picture photography. 
   If YES in step S 1003 , the CPU  115   a  checks whether a focus lens  105  stays in almost the same area for a predetermined time or longer in AF processing in moving picture photography, in other words, whether the focus lens  105  repeats direction reversal a predetermined number of times or more in almost the same area (step S 1004 ). 
   If YES in step S 1004 , this means that an in-focus position has been detected by the preceding AF processing in moving picture photography. The CPU  115   a  moves the focus lens  105  to a position corresponding to the maximum AF evaluation value obtained by the preceding AF processing in moving picture photography (step S 1005 ). The CPU  115   a  records a still picture by controlling a camera signal processing circuit  108  and still picture recording device  116  (step S 1006 ), and ends AF processing in still picture photography (step S 1007 ). 
   If NO in step S 1004 , the CPU  115   a  advances to step S 1008 , and checks whether the current lens position is near an in-focus position. This determination processing is performed based on the ratio of a luminance difference component and high-frequency component. 
   If the CPU  115   a  determines in step S 1008  that the current lens position is near an in-focus position, i.e., the focus lens  105  is slightly in an out-of-focus state, the CPU  115   a  executes fine driving in  FIG. 4 , and searches for a peak position (step S 1009 ). After that, the CPU  115   a  checks whether the focus lens  105  repeats direction reversal a predetermined number of times or more in almost the same area in fine driving processing of step S 1009  (step S 1010 ). 
   If NO in step S 1010 , this means that any in-focus position has not been detected yet by fine driving processing of step S 1009 . The CPU  115   a  returns to step S 1009 , and continues fine driving processing. 
   If YES in step S 1010 , this means that an in-focus position has been detected by fine driving processing of step S 1009 . The CPU  115   a  moves the focus lens  105  to a lens position corresponding to the maximum AF evaluation value obtained by fine driving processing (step S 1011 ). The CPU  115   a  records a still picture by controlling the camera signal processing circuit  108  and still picture recording device  116  (step S 1012 ), and ends AF processing in still picture photography (step S 1013 ). 
   If the CPU  115   a  determines in step S 1008  that the current lens position is not near an in-focus position, i.e., the focus lens  105  is greatly in an out-of-focus state, the CPU  115   a  moves the focus lens  105  to the closest focusing (wide-angle) direction at a high speed (step S 1014 ), and checks whether the AF evaluation value decreases (step S 1015 ). If NO in step S 1015 , the CPU  115   a  returns to step S 1014 , and continues lens moving processing to the closest focusing direction. 
   If YES in step S 1015 , the CPU  115   a  moves the focus lens  105  to the infinity (telephoto) direction at a high speed (step S 1016 ). The CPU  115   a  monitors changes in AF evaluation value, and checks whether the AF evaluation value exceeds its peak (step S 1017 ). If NO in step S 1017 , the CPU  115   a  returns to step S 1016 , and continues lens moving processing to the infinity direction. 
   If YES in step S 1017 , the CPU  115   a  moves the focus lens  105  to the peak position (in-focus position) (step S 1018 ). The CPU  115   a  performs processes in step S 1109  and subsequent steps. 
   In the second embodiment, when an in-focus position is considered to be detected by the preceding moving picture AF processing upon reception of a still picture photographing/recording instruction, the focus lens  105  is quickly moved to the in-focus position, AF processing is stopped, and a still picture is recorded. The second embodiment can realize photography free from any shutter time lag. 
   When the focus lens  105  is not located near an in-focus position (is greatly in an out-of-focus state) in the preceding moving picture AF processing upon reception of a still picture photographing/recording instruction, an in-focus position is immediately detected, the focus lens  105  is moved to the in-focus position, AF processing is stopped, and a still picture is recorded. Even if the focus lens  105  is greatly in an out-of-focus state in release operation for a still picture, a still picture free from any blur can be recorded as quickly as possible. 
   When the focus lens  105  is located near an in-focus position (is slightly in an out-of-focus state) in the preceding moving picture AF processing upon reception of a still picture photographing/recording instruction, an in-focus position is detected by fine driving, the focus lens  105  is moved to the in-focus position, AF processing is stopped, and a still picture is recorded. Hence, a still picture free from any blur can be quickly recorded. 
   Third Embodiment 
   AF processing in still picture photography according to the third embodiment will be described with reference to the flow charts of  FIGS. 12 and 13 . 
   The third embodiment considers the following situation. In the first and second embodiments, the focus lens  105  is located at an in-focus point with high possibility when the focus lens  105  performs direction reversal a predetermined number of times or more in the same area in moving picture AF processing. For this reason, when a still picture photographing/recording instruction is issued, AF operation is switched in accordance with whether the focus lens  105  repeats direction reversal a predetermined number of times or more in the same area in moving picture AF processing. 
   The depth of field is shallower on the telephoto side than on the wide-angle side. On the telephoto side, the in-focus range is narrower than on the wide-angle side, and the blur probability is higher. If the number of direction reversal operations for in-focus determination is equal between the telephoto side and the wide-angle side, like the first and second embodiments, a blur occurs on the telephoto side at high possibility with a small number of direction reversal operations for in-focus determination. With a large number of direction reversal operations, a blur hardly occurs on the telephoto side, but the number of in-focus point detection processes is increased on the wide-angle side. 
   To solve this problem, the third embodiment performs the following AF processing. 
   More specifically, after AF processing starts (step S 1201 ), a CPU  115   a  of an AF microcomputer  115  performs AF processing in moving picture photography described with reference to  FIGS. 3 to 7  (step S 1202 ). The CPU  115   a  checks whether a still picture release switch  118  has been turned on to input a still picture release signal (step S 1203 ). If NO in step S 1203 , the CPU  115   a  returns to step S 1202 , and continues AF processing in moving picture photography. 
   If YES in step S 1203 , the CPU  115   a  checks whether the current position of a focus lens  105  is on the telephoto side (step S 1204 ). If YES in step S 1204 , the CPU  115   a  checks whether the focus lens  105  stays in almost the same area for a predetermined time or longer in AF processing in moving picture photography, in other words, whether the focus lens  105  repeats direction reversal a predetermined number of times (N times) or more in almost the same area (step S 1205 ). 
   If YES in step S 1205 , this means that an in-focus position has been detected by the preceding AF processing in moving picture photography. The CPU  115   a  moves the focus lens  105  to a position corresponding to the maximum AF evaluation value obtained by the preceding AF processing in moving picture photography (step S 1206 ). The CPU  115   a  records a still picture by controlling a camera signal processing circuit  108  and still picture recording device  116  (step S 1207 ), and ends AF processing in still picture photography (step S 1208 ). 
   If NO in step S 1205 , this means that any in-focus position has not been detected yet by the preceding AF processing in moving picture photography. The CPU  115   a  advances to step S 1210 , and moves the focus lens  105  to the closest focusing (wide-angle) direction at a high speed. 
   If NO in step S 1204 , the CPU  115   a  checks whether the focus lens  105  repeats direction reversal a predetermined number of times (M times: N&gt;M) or more in almost the same area (step S 1209 ). By setting N&gt;M, the focus lens  105  is determined to be in focus for a large number of direction reversal operations on the telephoto side where the depth of field is shallow. On the wide-angle side where the depth of field is large, the focus lens  105  is determined to be in focus for a smaller number of direction reversal operations than on the telephoto side. This setting can increase the in-focus/out-of-focus determination precision on both the telephoto and wide-angle sides. 
   If YES in step S 1209 , this means that an in-focus position has been detected by the preceding AF processing in moving picture photography, and the CPU  115   a  shifts to step S 1206  and subsequent steps. If NO in step S 1209 , this means that any in-focus position has not been detected yet by the preceding AF processing in moving picture photography. The CPU  115   a  advances to step S 1210 , and moves the focus lens  105  to the closest focusing (wide-angle) direction at a high speed. 
   After moving the focus lens  105  to the closest focusing (wide-angle) direction at a high speed, the CPU  115   a  checks whether the AF evaluation value decreases (step S 1211 ). If NO in step S 1211 , the CPU  115   a  returns to step S 1210 , and continues lens moving processing to the closest focusing direction. 
   If YES in step S 1211 , the CPU  115   a  moves the focus lens  105  to the infinity (telephoto) direction at a high speed (step S 1212 ). The CPU  115   a  monitors changes in AF evaluation value, and checks whether the AF evaluation value exceeds its peak (step S 1213 ). If NO in step S 1213 , the CPU  115   a  returns to step S 1212 , and continues lens moving processing to the infinity direction. 
   If YES in step S 1213 , the CPU  115   a  moves the focus lens  105  to the peak position (in-focus position) (step S 1214 ). The CPU  115   a  performs fine driving in  FIG. 4 , and searches for a peak position (step S 1215 ). Fine driving processing is done in consideration of a case in which an actual in-focus position includes an error even if a peak position is detected during high-speed driving, or a case in which an object to be photographed moves. 
   The CPU  115   a  checks whether the focus lens  105  repeats direction reversal a predetermined number of times (arbitrary in this case) or more in almost the same area in fine driving processing of step S 1215  (step S 1216 ). 
   If NO in step S 1216 , this means that any in-focus position has not been detected yet by fine driving processing of step S 1215 . The CPU  115   a  returns to step S 1215 , and continues fine driving processing. 
   If YES in step S 1216 , this means that an in-focus position has been detected by fine driving processing of step S 1215 . The CPU  115   a  moves the focus lens  105  to a lens position corresponding to the maximum AF evaluation value obtained by fine driving processing (step S 1217 ). The CPU  115   a  records a still picture by controlling the camera signal processing circuit  108  and still picture recording device  116  (step S 1218 ), and ends AF processing in still picture photography (step S 1219 ). 
   In this manner, the third embodiment can increase the in-focus/out-of-focus determination precision by changing the in-focus determination threshold (number of direction reversal operations) in accordance with a focal length set when a still picture photographing/recording instruction is issued. 
   Similar to the first embodiment, when an in-focus position is considered to be detected by the preceding moving picture AF processing, the focus lens  105  is quickly moved to the in-focus position, AF processing is stopped, and a still picture is recorded. Photographing free from any shutter time lag can be achieved. If an in-focus position is considered not to be detected by the preceding moving picture AF processing upon reception of a still picture photographing/recording instruction, an in-focus position is immediately detected, the focus lens  105  is moved to the in-focus position, AF processing is stopped, and a still picture is recorded, thereby preventing recording any blurred still picture. 
   Fourth Embodiment 
   AF processing in still picture photography according to the fourth embodiment will be described with reference to the flow charts of  FIGS. 14 and 15 . 
   The fourth embodiment considers the following situation. In the first and second embodiments, the number of direction reversal operations used for in-focus determination processing performed immediately after a still picture photographing/recording instruction is issued, and the number of direction reversal operations used for in-focus determination processing performed after fine driving processing for newly detecting an in-focus point are set to the same value. 
   If, however, the number of direction reversal operations for in-focus determination is set to a small value, the in-focus position is erroneously determined and the focus lens may stop in an out-of-focus state in in-focus determination processing performed immediately after a still picture photographing/recording instruction is issued. If the number of direction reversal operations is set to a large value in order to avoid the stop in the out-of-focus state, the time taken to newly detect an in-focus point is prolonged. 
   To solve this problem, the fourth embodiment performs the following AF processing. 
   More specifically, after AF processing starts (step S 1401 ), a CPU  115   a  of an AF microcomputer  115  performs AF processing in moving picture photography described with reference to  FIGS. 3 to 7  (step S 1402 ). The CPU  115   a  checks whether a still picture release switch  118  has been turned on to input a still picture release signal (step S 1403 ). If NO in step S 1403 , the CPU  115   a  returns to step S 1402 , and continues AF processing in moving picture photography. 
   If YES in step S 1403 , the CPU  115   a  checks whether a focus lens  105  stays in almost the same area for a predetermined time or longer in AF processing in moving picture photography, in other words, whether the focus lens  105  repeats direction reversal a predetermined number of times (N times) or more in almost the same area (step S 1404 ). 
   If YES in step S 1404 , this means that an in-focus position has been detected by the preceding AF processing in moving picture photography. The CPU  115   a  moves the focus lens  105  to a position corresponding to the maximum AF evaluation value obtained by the preceding AF processing in moving picture photography (step S 1405 ). The CPU  115   a  records a still picture by controlling a camera signal processing circuit  108  and still picture recording device  116  (step S 1406 ), and ends AF processing in still picture photography (step S 1407 ). 
   If NO in step S 1404 , this means that any in-focus position has not been detected yet by the preceding AF processing in moving picture photography. The CPU  115   a  moves the focus lens  105  to the closest focusing (wide-angle) direction at a high speed (step S 1408 ), and checks whether the AF evaluation value decreases (step S 1409 ). If NO in step S 1409 , the CPU  115   a  returns to step S 1408 , and continues lens moving processing to the closest focusing direction. 
   If YES in step S 1409 , the CPU  115   a  moves the focus lens  105  to the infinity (telephoto) direction at a high speed (step S 1410 ). The CPU  115   a  monitors changes in AF evaluation value, and checks whether the AF evaluation value exceeds its peak (step S 1411 ). If NO in step S 1411 , the CPU  115   a  returns to step S 1410 , and continues lens moving processing to the infinity direction. 
   If YES in step S 1411 , the CPU  115   a  moves the focus lens  105  to the peak position (in-focus position) (step S 1412 ). The CPU  115   a  performs fine driving in  FIG. 4 , and searches for a peak position (step S 1413 ). Fine driving processing is done in consideration of a case in which an actual in-focus position includes an error even if a peak position is detected during high-speed driving, or a case in which an object to be photographed moves. 
   Then, the CPU  115   a  checks whether the focus lens  105  repeats direction reversal a predetermined number of times (M times: N&gt;M) or more in almost the same area (step S 1414 ). 
   In this fashion, the number (N times) of direction reversal operations used for in-focus determination processing performed immediately after a still picture photographing/recording instruction is issued is set larger than the number (M times) of direction reversal operations used for in-focus determination processing performed after fine driving processing for newly detecting an in-focus point. This is because the focus lens  105  is located near an in-focus point at higher probability after fine driving processing executed to newly detect an in-focus point than immediately after a still picture photographing/recording instruction is issued. 
   With N&gt;M, the stop in the out-of-focus state due to erroneous determination can be avoided in in-focus determination processing performed immediately after a still picture photographing/recording instruction is issued. The next in-focus point detection processing can also be quickly achieved. 
   If NO in step S 1414 , this means that any in-focus position has not been detected yet by fine driving processing in step S 1413 . The CPU  115   a  returns to step S 1413 , and continues fine driving processing. 
   If YES in step S 1414 , this means that an in-focus position has been detected by fine driving processing in step S 1413 . The CPU  115   a  moves the focus lens  105  to a lens position corresponding to the maximum AF evaluation value obtained by fine driving processing (step S 1415 ). The CPU  115   a  records a still picture by controlling the camera signal processing circuit  108  and still picture recording device  116  (step S 1416 ), and ends AF processing in still picture photography (step S 1417 ). 
   In the fourth embodiment, the number (N times) of direction reversal operations used for in-focus determination processing performed immediately after a still picture photographing/recording instruction is issued is set larger than the number (M times) of direction reversal operations used for in-focus determination processing performed after fine driving processing for newly detecting an in-focus point. This setting can prevent the stop in the out-of-focus state due to erroneous determination in in-focus determination processing performed immediately after a still picture photographing/recording instruction is issued. The next in-focus point detection processing can also be quickly done. 
   The present invention is not limited to the first to fourth embodiments, and these embodiments can also be appropriately combined. The first to fourth embodiments use the number of reversal moving operations of the focus lens as in-focus information obtained in photographing a moving picture. Alternatively, the high-frequency component of a video signal from a CCD, or an in-focus degree evaluation value based on the ratio of the high-frequency component and a luminance difference component can also be used. 
   The embodiments of the present invention have been described above. The present invention is not limited to contents disclosed in each embodiment, and can be applied to any apparatus as far as functions disclosed in the appended claims or the functions of arrangements according to the embodiments can be achieved. 
   For example, the software and hardware arrangements of the above embodiments can be properly replaced. 
   The above embodiments and their technical elements may be combined, as needed. 
   In the present invention, arrangements disclosed in the appended claims, or all or some of the arrangements of the embodiments may form one apparatus, an apparatus coupled to another apparatus, or an element which constitutes an apparatus. 
   The present invention can also be applied to various cameras such as a video camera capable of photographing a still picture, an electronic camera including a digital camera, an interexchangeable photographing lens type camera, a single-lens reflex camera, a lens shutter camera, and a monitor camera, an image sensing apparatus other than the camera, an optical apparatus, another apparatus, an apparatus, method, and computer program applied to the camera, image sensing apparatus, optical apparatus, and another apparatus, and elements which constitute them. 
   As has been described above, the above-described embodiments enable quickly photographing an in-focus still picture and improve the autofocus performance in photographing a still picture. 
   As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Technology Category: 3