JP4801960B2 - Autofocus control device, image forming apparatus using the autofocus control device, and autofocus control method - Google Patents

Description

  The present invention relates to an autofocus control device, an image forming apparatus, and an autofocus control method, and more particularly, to an improvement in focus control using a so-called contrast evaluation type autofocus (AF).

  Conventionally, an image forming apparatus such as a still camera or a video camera is equipped with an AF control apparatus that automatically and optimally adjusts the focus state of a subject image.

  Various types of AF control have been developed. In so-called digital still cameras and digital video cameras equipped with an imaging device such as a CCD or CMOS that can take out a projected image as a signal in real time. In contrast, AF of contrast evaluation method has been put into practical use.

  Here, the AF control of the contrast evaluation method utilizes the fact that the image contrast is high in an appropriate in-focus state. From the image data obtained by the imaging device, a high-frequency component of spatial frequency or between adjacent pixels is used. Is obtained as an AF evaluation value indicating the degree of focus.

  When the subject is in an appropriate in-focus state, the AF evaluation value is large because the sharpness of the subject image is high. When the subject is in an in-focus state, the sharpness of the subject is low and the AF evaluation value is small. Become.

  Therefore, the focus optical system such as a lens (or an image sensor such as a CCD or CMOS) is moved little by little from one end side to the other end side of the movable range along the optical axis direction. An AF evaluation value is calculated in real time for each movement, and the AF evaluation value after the movement and the AF evaluation value before the movement are sequentially compared, and the position where the AF evaluation value is maximized (the moving position of the focus optical system or the imaging device) (The moving position of the imaging device in the case of moving the image side) is determined by trial and error, the position where the AF evaluation value is maximized is determined as the optimum focusing position, and the determined optimum focusing position is determined. This is AF control for moving the focus optical system (or imaging device) (Patent Document 1).

  This contrast evaluation AF control is also referred to as hill-climbing AF control or CCDAF control.

  By the way, according to the above-mentioned Patent Document 1, since the AF evaluation value is calculated in almost the entire movable range of the focus optical system or the imaging device, a shooting start request operation (such as pressing the shutter release button) by the operator is performed. There arises a problem that the release time lag from the timing to the timing at which the AF control operation is completed and the actual shooting (start of imaging) is performed becomes longer.

  In addition, since the energy consumed by the motor for moving the focus optical system or the imaging device increases as the movement length increases, a substantial image is taken with a digital still camera using a battery as a power source. There is also a problem that the possible time is shortened.

  Therefore, a control method has been proposed in which the search range is limited to a predetermined range among all movable ranges of the focus optical system or the like (Patent Document 2).

In addition, an operation content for limiting the search range as such (Patent Document 3), or a movable range is divided, and any one of a plurality of small ranges obtained by dividing the range is obtained. Specify whether the range is designated as a search range (Patent Document 4), or whether or not the movable range of the focus optical system is classified into a permitted range and a prohibited range. A technique (Patent Document 5) that prevents the area from being located in a region has been proposed.
Japanese Examined Patent Publication No. 39-5265 JP 54-113334 A Japanese Patent Laid-Open No. 2003-230039 JP 2003-262786 A JP-A-9-212298

  However, any of the techniques described in any of the above-mentioned patent documents is only a technique for narrowing the search range from the movable range, and does not require a search. Rather, even with the technique for narrowing the search range in this way, the optimum in-focus position to be obtained does not always exist in the narrowed search range. The optimum focusing state cannot be obtained, and the photographing operation cannot be completed.

  Moreover, even if the search range is limited in this way, the search time cannot be significantly shortened. If the possibility of taking the risks described above is taken into consideration, the search range is not narrowed, but the entire movable range is searched. It is preferable to reduce the time required for the search while setting the target candidate.

  The present invention has been made in view of the above circumstances, and the time required for searching for the in-focus position while using the focus optical system or the imaging device system as a search target candidate for the entire movable range in the direction along the optical axis. An object of the present invention is to provide an autofocus control device, an autofocus control method, and an image forming apparatus that can shorten the image forming time.

  When an actual shooting start operation such as pressing a shutter release button (shooting start operation input means) is input, the auto focus control device, the control method, and the image forming apparatus, the focus optical system or the imaging device When the movement starts from one end side to the other end side of the movable range, the AF evaluation value for each of these moving positions is calculated as needed, and the AF evaluation value reaches a maximum value (maximum value). The moving position of the focus optical system or the imaging device is searched for as the optimum focusing position. However, the autofocus control device, the control method, and the image forming device according to the present invention are not yet input before the actual shooting start operation is input. From this, the AF evaluation value is calculated as needed, the AF evaluation value calculated immediately before the actual shooting start operation is input, and a preset threshold value In comparison, based on the result of this comparison, it is determined from which end of the movable range the movement (search operation for the displacement position corresponding to the optimum in-focus state) starts, and the determined end After being displaced at once, AF control of the contrast evaluation method is performed from the one end to the other end.

That is, the autofocus control device according to the present invention includes a drive unit that displaces at least one of a focus optical system and an imaging device that captures an image projected through the focus optical system within a movable range thereof, and the imaging device. On the basis of the image data obtained corresponding to the image projected onto the image, an evaluation value calculating means for calculating an autofocus evaluation value representing the degree of focus of the image in the imaging device and an operation for starting shooting are input. When the shooting start operation is input to the shooting start operation input unit and the shooting start operation input unit, at least one of the focus optical system and the imaging device is set to one of the movable ranges. After the movement to the end, while controlling the drive means to displace from the end toward the other end, The evaluation value calculation means is controlled to calculate the autofocus evaluation value at every predetermined timing, and the image corresponding to the optimum focus state of the image based on each obtained autofocus evaluation value e Bei and control means for searching for a displaced position, and wherein, prior to the input of the start of photographing operation to the photographing start operation input means, the acquired auto focus evaluation value, the acquired auto focus the comparison between the evaluation value and the pre-Me set predetermined threshold and performed at predetermined time intervals, when the operation of the photographing start has been performed, the results of the comparisons at the time the operation is input to the imaging start based on the time autofocus evaluation value is greater than the predetermined threshold value, of the two ends of the movable range, select the end towards the moving distance is short, the autofocus When the evaluation value is not greater than the predetermined threshold, one of the two ends of the movable range, and selects the end towards the moving distance is not shorter.

  Here, the focus optical system may be a single focus lens or a lens group in which the focus lens and another optical system such as a zoom optical system are integrally formed.

  An imaging device refers to a device that can extract an image signal in substantially real time, as represented by a CCD or a CMOS.

  As the driving means, for example, a pulse motor or the like can be applied.

  For the autofocus evaluation value, a spatial frequency high-frequency component of the image projected on the imaging device or an integrated value of the luminance difference between adjacent pixels can be used. In the case of an evaluation value using these, the value is large. This means that the degree of focus is high as the time goes.

  The shooting start operation input means corresponds to, for example, a shutter release button or the like in the camera, and may be any device that can be input by the user as an operation to start shooting.

  The predetermined threshold value is related to the autofocus evaluation value at each displacement position, and the spatial distance between the displacement position corresponding to the optimum focus state and the displacement position corresponding to the autofocus evaluation value is a perspective. It is set as a value suitable for comparison, and depending on whether the autofocus evaluation value is greater than or less than this predetermined threshold, the current displacement position is close to or close to the optimum focus position It can be determined whether there is any.

  Further, the threshold value is not limited to one, and for example, two values of large and small can be adopted. The relatively large value is set as the first threshold value, and the relatively small value is set as the second threshold value. Whether the autofocus evaluation value is larger than the first threshold value or not larger than the first threshold value is set as the first threshold value. It may be determined whether or not it is larger than two threshold values.

  The predetermined timing in the control of the evaluation value calculation means by the control means may be time-series timing (for example, timing at a constant time interval), or timing corresponding to a spatial position (constant optical system). It may be a timing every time the rotation angle position is passed, or a timing for every fixed feed amount of the optical system). Moreover, those time intervals, angles, and feed amounts may not be constant.

  Since the timing of the shooting start operation is the timing at which an operation by the user is input, after detecting the shooting start operation, the control prior to the shooting start operation by the control means is started retroactively from this detection time. In practice, for example, when the energization of the autofocus control device is turned on, or when a predetermined time has elapsed after turning on (for example, during an initialization period after the energization is turned on). The control means starts the control prior to the shooting start operation by a process that is always performed prior to the shooting start operation (such as a period during which shooting cannot be started).

  According to the autofocus control device according to the present invention configured as described above, the control means obtains the autofocus evaluation value prior to the shooting start operation. Therefore, the autofocus is not performed until the shooting start operation is input. The displacement position corresponding to the optimum in-focus state can be detected earlier than that for calculating the evaluation value.

  The calculated autofocus evaluation value is compared with a predetermined threshold value by the control means, and this predetermined threshold value determines the proximity between the current displacement position and the displacement position corresponding to the optimum in-focus state. Because of this value, a result of determination as to whether or not it is close to the optimum focus position is obtained by this comparison even at the time of the photographing start operation.

  Here, when a shooting start operation is detected, the driving means moves at least one of the focus optical system and the imaging device to one end of the movable range. As described above, the end of is determined in accordance with the proximity between the current displacement position and the displacement position corresponding to the optimum in-focus state.

  For example, when the displacement position in the shooting start operation is close to the displacement position corresponding to the optimum focus state, the end closer to the displacement position in the shooting start operation is selected, and the displacement position in the shooting start operation and the optimum focus are selected. When the displacement position corresponding to the state is not close, the end portion that is not close to the displacement position in the photographing start operation is selected.

  First, at least one of the focus optical system and the imaging device is displaced at a stroke toward the selected end. At the time of displacement toward the selected end portion, the autofocus evaluation value is not calculated at every predetermined timing, so the focus optical system and the imaging device At least one of them can be displaced.

  After reaching the selected end, the search for the displacement position corresponding to the optimum focus state is started toward the end not selected, but the displacement operation in this search is selected. Unlike the case of the first displacement operation that is displaced toward the end, in order to calculate the autofocus evaluation value sequentially at each predetermined timing, and to compare the size of the calculated autofocus evaluation value and the threshold, It takes a longer time than the first displacement operation.

  However, in the autofocus control device according to the present invention, the end portion to be displaced first is selected depending on whether or not the displacement position in the photographing start operation is close to the displacement position corresponding to the optimum focus state. Therefore, the selected end portion is closer to the displacement position corresponding to the optimum in-focus state than the other end portion, and therefore, the displacement position corresponding to the optimum in-focus state is searched earlier than the conventional one. Can do.

  Note that the displacement operation to the first end is extremely fast compared to the displacement operation during the search operation, so that the image capture start is based on the comparison result between the autofocus evaluation value and the threshold value during the image capture start operation. Even if it is displaced from the displacement position at the time of operation to the far end, there is no significant difference in elapsed time compared to the case of being displaced to the near end.

  The search operation for the displacement position corresponding to the optimum in-focus state does not mean that the search range is made narrower than the movable range of at least one of the focus optical system and the imaging device. It is possible to avoid the worst situation in which an optimum in-focus state cannot be acquired, which may occur in the case of narrowing.

  Note that the threshold value is not limited to one. For example, two threshold values (a first threshold value and a second threshold value smaller than the first threshold value) can be applied.

  According to the autofocus control device of the present invention configured as described above, when the autofocus evaluation value obtained prior to the shooting start operation is larger than a predetermined threshold, that is, the displacement position at the time of the shooting start operation is When close to the displacement position corresponding to the optimum focus state, the end portion with the shorter moving distance is selected from the two end portions of the movable range during the shooting start operation. Corresponding displacement positions are also present in the two ends of the movable range near the end with the shorter moving distance during the shooting start operation. The time required for the search operation can be shortened.

  Conversely, when the autofocus evaluation value obtained prior to the shooting start operation is not greater than the predetermined threshold, that is, when the displacement position at the time of the shooting start operation is not close to the displacement position corresponding to the optimum focus state Is selected from the two ends of the movable range, the end of which the moving distance is not short in the shooting start operation, but the displacement position corresponding to the optimum focus state is the two ends of the movable range. The time required for the search operation after shifting to this non-short end is shortened because it is present near the end where the moving distance is not short during the shooting start operation. can do.

  The threshold value is preferably changed according to the focal length of the focus optical system.

  According to the autofocus control device according to the present invention configured as described above, the focal depth changes according to the focal length. However, as the focal depth is shallower, the deviation from the displacement position corresponding to the optimum in-focus state ( The fluctuation ratio of the autofocus evaluation value with respect to the deviation along the optical axis) is large (the degree of correlation between the displacement position and the autofocus value is high), and the detection accuracy of the displacement position corresponding to the optimal focus state is improved. Can do.

  Furthermore, the control means may control the aperture diameter for limiting the light beam passing through the focus optical system to be maximum on the open side when obtaining the autofocus evaluation value prior to the photographing start operation. preferable.

  According to the autofocus control device according to the present invention configured as described above, the depth of focus can be reduced by opening the aperture to the maximum, and the deviation from the displacement position corresponding to the optimum in-focus state (optical axis) The variation rate of the autofocus evaluation value with respect to the amount of deviation along the distance (the amount of deviation along the axis) is large (the degree of correlation between the displacement position and the autofocus value is high), and the detection accuracy of the displacement position corresponding to the optimum focus state can be improved. .

  An image forming apparatus according to the present invention includes the autofocus control device according to the present invention.

  Here, the image forming apparatus includes a still camera, a video camera, an image scanner, a copying machine, a portable information terminal, and the like.

  According to the image forming apparatus according to the present invention configured as described above, it is possible to exhibit the corresponding effects exhibited by the above-described autofocus control apparatuses according to the present invention.

The autofocus control method according to the present invention includes at least one of a focus optical system and an imaging device that outputs image data corresponding to an image projected through the focus optical system. After moving to the end portion, while controlling to be displaced from the end portion toward the other end portion, at each predetermined timing during the displacement period, the image pickup device in the imaging device based on the image data An autofocus control method for controlling to calculate an autofocus evaluation value representing the degree of focus of an image and searching for the displacement position corresponding to the optimum focus state of the image based on the obtained autofocus evaluation values in Standing earlier photographing start operation, the acquired auto focus evaluation value, the auto-focus evaluation value and the pre-Me settings the acquired Performs a comparison with a predetermined threshold value which is a predetermined time interval, the when the start of photographing operation is performed, based on the results of the comparisons at the time of the photographing start operation is performed, the autofocus When the evaluation value is larger than the predetermined threshold value , an end portion having a shorter moving distance is selected from the two end portions of the movable range, and the autofocus evaluation value is not larger than the predetermined threshold value. In some cases, one of the two end portions of the movable range that is not short is selected.

  According to the autofocus control method according to the present invention configured as described above, the first displacement is determined according to whether or not the displacement position in the shooting start operation is close to the displacement position corresponding to the optimum in-focus state. Since the end portion is selected, the selected end portion is closer to the displacement position corresponding to the optimum focus state than the other end portion, and accordingly, the displacement position corresponding to the optimum focus state is conventionally set. You can search faster.

  Note that the displacement operation to the first end is extremely fast compared to the displacement operation during the search operation, so that the image capture start is based on the comparison result between the autofocus evaluation value and the threshold value during the image capture start operation. Even if it is displaced from the displacement position at the time of operation to the far end, there is no significant difference in elapsed time compared to the case of being displaced to the near end.

  The search operation for the displacement position corresponding to the optimum in-focus state does not mean that the search range is made narrower than the movable range of at least one of the focus optical system and the imaging device. It is possible to avoid the worst situation in which an optimum in-focus state cannot be acquired, which may occur in the case of narrowing.

  According to the autofocus control method of the present invention configured as described above, when the autofocus evaluation value obtained prior to the shooting start operation is larger than a predetermined threshold, that is, the displacement position at the time of the shooting start operation is When close to the displacement position corresponding to the optimum focus state, the end portion with the shorter moving distance is selected from the two end portions of the movable range during the shooting start operation. Corresponding displacement positions are also present in the two ends of the movable range near the end with the shorter moving distance during the shooting start operation. The time required for the search operation can be shortened.

  Conversely, when the autofocus evaluation value obtained prior to the shooting start operation is not greater than the predetermined threshold, that is, when the displacement position at the time of the shooting start operation is not close to the displacement position corresponding to the optimum focus state Is selected from the two ends of the movable range, the end of which the moving distance is not short in the shooting start operation, but the displacement position corresponding to the optimum focus state is the two ends of the movable range. The time required for the search operation after shifting to this non-short end is shortened because it is present near the end where the moving distance is not short during the shooting start operation. can do.

  Further, it is preferable to vary the threshold value according to the focal length of the focus optical system.

  According to the autofocus control method according to the present invention configured as described above, the focal depth changes according to the focal length. However, as the focal depth is shallower, the shift from the displacement position corresponding to the optimum in-focus state ( The fluctuation ratio of the autofocus evaluation value with respect to the deviation along the optical axis) is large (the degree of correlation between the displacement position and the autofocus value is high), and the detection accuracy of the displacement position corresponding to the optimal focus state is improved. Can do.

  Furthermore, when obtaining the autofocus evaluation value prior to the photographing start operation, it is preferable to set the aperture diameter for limiting the light beam passing through the lens to open.

  According to the autofocus control method according to the present invention configured as described above, the depth of focus can be reduced by opening the diaphragm to the maximum, and the deviation (optical axis) from the displacement position corresponding to the optimum in-focus state can be achieved. The variation rate of the autofocus evaluation value with respect to the amount of deviation along the distance (the amount of deviation along the axis) is large (the degree of correlation between the displacement position and the autofocus value is high), and the detection accuracy of the displacement position corresponding to the optimum focus state can be improved. .

  The macro autofocus control method according to the present invention is characterized in that the autofocus control method according to the present invention is applied to a macro autofocus control method to which a macro shooting mode for shooting a subject at a close distance is applied. And

  According to the macro autofocus control method according to the present invention configured as described above, the feed amount of the focus optical system is larger than that of a focus optical system that is not a macro system, and therefore the autofocus control method of the present invention is applied. Thus, the effect of reducing the time lag can be more effectively exhibited.

  According to the autofocus control device, the image forming apparatus, and the autofocus control method according to the present invention, the displacement position corresponding to the optimum in-focus state can be searched earlier than before.

  In addition, the search operation for the displacement position corresponding to the optimum in-focus state is not performed by making the search range narrower than the movable range of at least one of the focus optical system and the imaging device. It is possible to avoid the worst situation in which an optimum in-focus state cannot be acquired, which may occur in the case of narrowing.

  Hereinafter, specific embodiments of an autofocus control device, an autofocus control method, and a digital still camera as an image forming apparatus according to the present invention will be described.

  1, 2, 3 and 4 are diagrams showing a configuration of a digital still camera according to an embodiment of the present invention. FIG. 1 is a block diagram showing an outline of an overall system configuration of the digital still camera. 1 to 4 are diagrams schematically showing an external configuration of the camera shown in FIG. 1, in which FIG. 2 is a plan view, FIG. 3 is a front view, and FIG. 4 is a rear view.

  The camera shown in FIG. 1 includes a photographic lens system 1 including a focus lens (focus optical system), a CCD 3 (imaging device) that captures an image projected through the photographic lens system 1, and a photographic lens system 1 and a CCD 3. A mechanical shutter 2 provided therebetween, a motor driver 19 that displaces at least the focus lens of the photographing lens system 1 within a movable range along the optical axis direction, and a shutter release button (to which photographing start operation is input) An operation unit 20 including a photographing start operation input unit), a signal processing unit 31 of a front end (F / E) mainly performing signal reading processing from the CCD 3, control for reading signals from the CCD 3, and reading Signal processing, motor driver 19 drive control, operation signal input processing from the operation unit 20, reading from the CCD 3 A configuration including a digital signal processing IC 32 (control unit) that performs various arithmetic processes such as an autofocus evaluation value that is an index value indicating the degree of focusing of an image represented by the image data based on the obtained image data It is.

  Here, the F / E signal processing unit 31 includes a CDS (correlated double sampling) circuit 4, an AGC (automatic gain control) circuit 5, an A / D (analog / digital) converter 6, and a timing generator (TG). 7 is provided.

  On the other hand, the digital signal processing IC 32 includes a CCD interface (CCD I / F) 8, a memory controller 9, a display output control unit 10, a compression processing unit 11, a YUV conversion unit 12, a resizing processing unit 13, and a media interface (media I / F). ) 14 and a CPU (Central Control Unit) 15, and a ROM (Read Only Memory) 16, a frame memory (SDRAM) 17, a liquid crystal (LCD) display 18, an audio output device 21, and a memory card 22 are connected. While controlling, it receives inputs such as signals from the distance measuring sensor 23, the operation unit 20, and the ROM 16.

  The CPU 15 functions as an evaluation value calculating means for calculating the autofocus evaluation value L, which is the index value described above. The calculation of the autofocus evaluation value L starts from the time when the camera is turned on. And performed at predetermined timings.

  Then, the CPU 15 compares the calculated autofocus evaluation value L with a predetermined threshold value, and based on the result of this comparison at the timing of the photographing start operation, the focus of the photographing lens system 1 is determined. It is determined which of the two end portions of the movable range the lens is to be moved.

  That is, pressing the shutter release button of the operation unit 20 is a shooting start operation, and the CPU 15 detects that the release button has been pressed, that is, an input of a shooting start operation, and the focus lens is moved to the focus lens. Each time this displacement occurs, the motor driver 19 is controlled so that the focus lens is gradually moved from one end to the other end of the movable range. The focus lens displacement position (focus position) when calculating the autofocus evaluation value and comparing the calculated autofocus evaluation value with the threshold value to obtain the optimal focus state of the image ), And the focus lens is moved to the position obtained by this search. Perform the F control.

  The mechanical shutter 2 is inserted on the optical path between the photographing lens system 1 and the CCD 3 to open and close the optical path and limit the exposure of the CCD 3. The CCD 3 converts an optical image incident on the light receiving surface in an exposed state into an electric signal, temporarily holds it, and transfers and outputs it as image data.

  The CDS circuit 4 performs correlated double sampling on the output image signal of the CCD 3. The AGC circuit 5 adjusts the correlated double sampling output of the CDS circuit 4 to a desired signal level by performing automatic gain control. The A / D converter 6 converts the analog output of the AGC circuit 5 into digital data.

  The timing generator (TG) 7 responds to a VD signal (vertical synchronization drive signal) and an HD signal (horizontal synchronization drive signal) which are synchronization drive signals given from the CCD interface 8 of the digital signal processing IC 32, and In cooperation, timing signals are given to the CCD 3, the CDS circuit 4, the AGC circuit 5, and the A / D converter 6 to synchronize them appropriately.

  The signal processing IC 32 stores the digital image data given through the A / D converter 6 of the signal processing unit 31 in the frame memory 17 based on the control of the CPU 15, as well as required processing such as compression processing and YUV conversion processing. , And storing the data processed in the signal processing IC 32 in the frame memory 17, the image data supplied from the A / D converter 6, or taken out from the frame memory 17, etc. Display, compression processing of digital image data given from the A / D converter 6 or taken out from the frame memory 17, YUV conversion processing and resizing processing, and media interface of the digital image data taken out from the frame memory 17 14 to store data in the memory card 22 via 14.

  The CCD interface 8 receives digital image data supplied from the A / D converter 6 of the signal processing unit 31 and stores it in the frame memory 17 via the memory controller 9.

  Under the control of the CPU 15, the memory controller 9 receives RGB original data (RAW-RGB) given through the CCD interface 8, YUV data YUV converted by the YUV converter 12, and JPEG (Joint Photographic) by the compression processor 11. The writing to the frame memory 17 and the reading from the frame memory 17 such as JPEG data and OSD (on-screen display) image data compressed by the Experts Group method are controlled.

  The display output control unit 10 displays the image data read from the frame memory 17 on the LCD display 18 and outputs a TV output for display on an external television (TV) or the like.

  The compression processing unit 11 compresses the image data or the like given from the A / D converter 6 or taken out from the frame memory 17 by a predetermined compression method such as the JPEG method.

  The YUV conversion unit 12 performs YUV conversion on the image data given from the A / D converter 6 or taken out from the frame memory 17 in accordance with an auto white balance (AWB) control value given from the CPU 15.

  The resizing processing unit 13 resizes the image data given from the A / D converter 6 or taken out from the frame memory 17.

  The media interface 14 writes the image data given from the A / D converter 6 or taken out from the frame memory 17 to the memory card 22 under the control of the memory controller 9 and the CPU 15.

  That is, the memory controller 9 stores the image data given from the A / D converter 6 in the frame memory 17, takes out the image data from the frame memory 17, and displays it on the LCD display via the display output control unit 10. 18, the image data is taken out from the frame memory 17, compressed by the compression processing unit 11 such as JPEG method, YUV conversion by the YUV conversion unit 12, resizing processing by the resizing processing unit 13, and compression, YUV The data after conversion and resizing is used for writing to the frame memory 17, and the data is further extracted from the frame memory 17 and used for writing to the memory card 22.

  The ROM 16 stores an operation program, data, and the like of the CPU 15. The CPU 15 executes various processes related to the shooting operation and the above-described autofocus control process according to the program and data read from the ROM 16.

  The frame memory 17 is a semiconductor memory such as SDRAM (Synchronous Dynamic Random Access Memory), for example, and stores RGB original data, YUV converted YUV data, JPEG compressed JPEG data, OSD image data, and the like. , Store each.

  The LCD display 18 is a display device capable of displaying an image, such as a liquid crystal display device, and is supplied from the A / D converter 6 or taken out from the frame memory 17 and supplied via the display output control unit 10. Is displayed, and further, necessary information is displayed.

  The motor driver 19 drives a lens driving motor (shown as the motor driver 19) of the photographing lens system 1 for focusing, zooming, and the like based on the control of the CPU 15, and for shutter opening / closing operations. In conjunction with the timing generator 7, a shutter drive motor (not shown) of the mechanical shutter 2 is driven.

  The operation unit 20 includes a shutter release button, a mode switch for switching each mode, and at least a part of operation means such as other switches, keys, levers, and dials, and an operation instruction for the digital still camera, An operation for giving information such as a setting instruction and a selection instruction to the CPU 15 is performed.

  The voice output device 21 emits a voice such as an alarm and a voice announcement. The memory card 22 is a small IC memory type recording medium referred to as a small card incorporating a semiconductor non-volatile memory such as a so-called flash memory, and is an external recording medium that can be attached to and detached from the digital still camera. Usually, for example, it is used by being mounted in a slot provided in a digital still camera.

  For example, under the control of the CPU 15, the memory card 22 takes out image data compressed by a method such as JPEG in the frame memory 17 from the frame memory 17 via the memory controller 9 and stores it as a photographing result.

  The distance measuring sensor 23 constitutes distance measuring means for periodically measuring the subject distance by a so-called triangulation method using the distance measuring unit 105 shown in FIG.

  The CPU 15 monitors the change in the measured value of the subject distance by the distance measuring sensor 23 and determines whether or not the in-focus state is maintained. 2 to 4, the digital still camera has an LCD monitor 18A on the back of the body and a sub LCD 18B on the top of the body. The LCD monitor 18A and the sub LCD 18B are shown in FIG. The LCD display 18 is configured.

  The LCD monitor 18A mainly displays an image, and the sub LCD 18B mainly displays a film counter, various symbol marks indicating the date / time and operation state, and the like.

  A shutter release button 201 and a mode dial 202 are disposed on the upper surface of the body, and a wide angle side (WIDE) zoom switch 203, a telephoto side (TELE) zoom switch 204, a self-timer / deletion switch are disposed on the rear surface of the body. 205, a menu switch 206, an up / strobe switch 207, a right switch 208, a display switch 209, a down / macro switch 210, a left / image confirmation switch 211, and an OK (OK) switch 212. However, the operation unit 20 in FIG. 1 is configured.

  A power switch 101 is disposed at the lower back of the body, and a memory card / battery cover that covers a memory card 22 such as an SD card and a battery storage unit as a power source is provided on the right side of the body facing the subject. 102 is disposed.

  On the front surface of the body, a strobe light emitting unit 103, an objective surface of the optical viewfinder 104, a distance measuring unit 105, a remote control (remote control) light receiving unit 106, a lens barrel unit 107 of a photographing lens, and the like are arranged.

  Further, an eyepiece portion of the optical viewfinder 104, an AF display LED (light emitting diode) 108, and a strobe display LED 109 are disposed on the back side of the body.

  In addition, AF evaluation values obtained corresponding to the sharpness of the edge portion of the subject image (corresponding to the high frequency component of the spatial frequency component) from the video signal are sequentially acquired while moving the focus lens, and the AF evaluation value Focus control means that stops the focus lens with the local maximum as the focal point, and performs automatic focusing operation.When shooting in macro mode, if a predetermined condition is met, Range control means for limiting the movement range of the focus lens to a range narrower than the focus range and performing automatic focusing operation by the focusing control means, and at least one automatic focusing operation has been performed after setting the macro mode As a predetermined condition, and when the predetermined condition is satisfied, means for performing a focusing operation in a narrow range, means for monitoring the focusing state in the focusing control means, and previous automatic focusing Including the maintenance of the optimal focus state after the operation as a predetermined condition, and means for performing a focusing operation in a narrow range when the predetermined condition is satisfied, a means for monitoring a change in the measurement distance by the distance measurement means, Means for causing the focusing operation to be performed in a narrow range when a predetermined condition is satisfied, wherein the change in the measured distance after the automatic focusing operation is equal to or less than a predetermined value; A luminance distribution measuring means for measuring the distribution, a means for monitoring a change in the luminance distribution by the luminance distribution measuring means, and the change in the luminance distribution after the previous automatic focusing operation is a predetermined amount or less as the predetermined condition. When the predetermined condition is satisfied, the means for performing the focusing operation in a narrow range, the means for monitoring the AF evaluation value in the focusing control means, and the change in the AF evaluation value after the previous automatic focusing operation is predetermined. Below the value When the predetermined condition is satisfied and the predetermined condition is satisfied, the means for performing the focusing operation in a narrow range, the means for monitoring the change of the zoom magnification in the imaging optical system, and the zoom magnification are changed The means for performing the focusing operation in the entire focusing range is realized by the above-described units being controlled by the CPU 15 or the like.

  First, an outline of the operation of this type of digital still camera will be described.

  By operating the mode dial 202 (see FIG. 2) of the operation unit 20 in FIG. 1 and setting the operation mode to “recording mode”, the digital still camera is activated in the recording mode.

  In the setting of the mode dial 202, the CPU 15 detects that the state of the mode switch included in the operation unit 20 is in the recording mode ON, and controls the motor driver 19 to control the photographing lens system 1 of the lens barrel unit 107. Move to a position where you can shoot.

  Further, power is turned on to the CCD 3, the signal processing unit 31, the LCD display 18, and the like to start the operation.

  When the power of each part is turned on, the operation in the finder mode is started. In this finder mode, the light that has entered the CCD 3 through the photographing lens system 1 is converted into an electrical signal, which is converted into an analog RGB signal composed of analog signals of R (red), G (green), and B (blue) as a CDS circuit. 4 and AGC circuit 5 are sequentially sent to A / D converter 6.

  Each signal converted into a digital RGB signal by the A / D converter 6 is converted into a YUV signal by the YUV converter 12 of the digital signal processing IC 32 and written into the frame memory 17 by the memory controller 9.

  The YUV signal is read by the memory controller 9 and output as a TV output via the display output control unit 10, or sent to the LCD display 18 to be displayed on the LCD monitor 18A. This process is usually performed at 1/30 second intervals and is displayed every 1/30 seconds, so that a finder mode display as a so-called electronic finder is displayed.

  Also, based on the digital RGB signal captured in the CCD interface 8 of the digital signal processing IC 32, an AF evaluation value indicating the degree of focus on the screen, an AE (automatic exposure) evaluation value for detecting subject brightness, and a subject color And an AWB (automatic white balance) evaluation value that detects.

  These calculated values are read out as feature data to the CPU 15 and used for each process of automatic focusing (AF), automatic exposure (AE), and automatic white balance (AWB).

  The AF evaluation value is calculated by, for example, the output integrated value of the high frequency component extraction filter or the integrated value of the luminance difference between adjacent pixels.

  In the in-focus state, the edge portion of the subject image is projected clearly, so that the high frequency component is the highest. Using this characteristic, during the focus detection operation by automatic focusing, AF evaluation values at various displacement positions of the focus lens are acquired, and the position where the AF evaluation value is maximized corresponds to the optimum focusing state. Automatic focusing control is executed as the displacement position.

  The AE evaluation value and the AWB evaluation value are created from the integrated values of the R signal, the G signal, and the B signal.

  For example, the screen is equally divided into 192 blocks, and the respective RGB integrated values are calculated. The CPU 15 reads the RGB integration values, calculates the brightness of each area in automatic exposure, and determines the control value for automatic exposure from the brightness distribution.

  In automatic white balance, a control value for automatic white balance that matches the color of the light source is determined from the RGB distribution. The automatic exposure and automatic white balance processes are continuously performed during the finder mode.

  When the shutter release button 201 in FIG. 2 is operated, an automatic focusing operation for detecting a focusing position and a still image recording process are performed.

  When the shutter release button 201 is pressed, a signal representing a still image shooting start operation is taken into the CPU 15 from the operation unit 20, and the CPU 15 synchronizes with the frame rate via the motor driver 19 at least in the shooting lens system 1. A part of the focus lens is driven, and contrast evaluation method (mountain climbing) AF control is executed.

  If the target range to search for the displacement position corresponding to the optimal focus state is the entire range from infinity to close, the focus lens moves to each focus position from close to infinity or from infinity to close Then, the CPU 15 reads the AF evaluation value at each frame (= each focus position) created by the digital signal processing IC 32.

  The focus lens is moved to the in-focus position with the point at which the AF evaluation value at each focus position is maximized as the in-focus position. The analog RGB signal extracted from the CCD 3 after completion of the automatic focusing is converted into a digital RGB signal and stored in the frame memory 17 via the digital signal processing IC 32. The digital RGB signal is read again by the digital signal processing IC 32, converted into YUV data, and written back to the frame memory 17.

  At the time of capturing a still image, YUV converted image data is sent to the compression processing unit 11 including an image compression / decompression circuit in the digital signal processing IC 32.

  The YUV data sent to the compression processing unit 11 is compressed and written back to the frame memory 17. The compressed data in the frame memory 17 is read out via the digital signal processing IC 32 and stored in a data storage memory such as the memory card 22.

  Next, operations that are characteristic of the digital still camera according to the present embodiment will be described in detail. FIG. 5 is a graph showing AF evaluation values for each focus position (displacement position of the focus lens) and AF evaluation values based on the subject distance.

  Here, a first threshold value A, which is a relatively large value, and a second threshold value B (<A) smaller than the first threshold value A are set in advance.

  In the shooting state, before the shutter release button is pressed, for example, immediately after the power is turned on, the AF evaluation value is continuously acquired in synchronization with the frame rate.

  The search operation covers the entire range (between both ends L1 and L2) of the focus lens movable range (L1 to L2 (where L2> L1)), but the focus lens corresponding to the optimum focus state In the displacement position (Lm), the autofocus evaluation value becomes a maximum, and the maximum value is one place in the entire movable range. In the direction approaching the displacement position Lm corresponding to the maximum value, the autofocus evaluation value is simply increased and becomes the maximum value. The direction away from the corresponding displacement position Lm is simply reduced. Therefore, when the maximum value can be detected during the search operation, the remaining range (Lm + α to L2 or Lm−α to L1; α The search operation is terminated without performing a search for> 0).

  Accordingly, when the displacement position corresponding to the maximum value (the displacement position corresponding to the optimum in-focus state) Lm is close to the end (L1 or L2) where the search operation is started (at least the movable range (L1 to L2)). The search operation can be terminated earlier according to the proximity of the entire image.

  On the contrary, when the displacement position corresponding to the maximum value (the displacement position corresponding to the optimum in-focus state) Lm is at a position far from the end (L1 or L2) where the search operation is started (at least the movable range (L1 to L2). ), The end of the search operation is delayed according to the distance.

  Here, in the camera of the present embodiment, since the CPU 15 compares the autofocus evaluation value and the predetermined thresholds A and B set in advance before the shooting start operation, even at the time of the shooting start operation. As a result of this comparison, it can be determined whether or not the displacement position L of the focus lens at the time of the photographing start operation is close to the displacement position corresponding to the maximum value (the displacement position corresponding to the optimum in-focus state) Lm. .

  When it is determined that the CPU 15 is close, that is, when the corresponding curve between the focus position L and the autofocus evaluation value is defined as shown in FIG. 5A (maximum value Lm), the autofocus evaluation value Is at the displacement position L3 corresponding to a value larger than the threshold value A (of course, larger than the threshold value B), the CPU 15 moves the focus lens at the time of the photographing start operation out of the two end portions of the movable range. Then, it is determined that the focus lens is moved to the end L1 having a shorter distance from the displacement position L3, and the motor driver 19 is controlled so as to actually move.

  On the other hand, when it is determined that the CPU 15 is not close, that is, when the autofocus evaluation value is at the displacement position L4 corresponding to a value smaller than the threshold B (of course, smaller than the threshold A), the CPU 15 starts photographing. The motor driver is determined to move the focus lens during operation to the end L1 which is farther from the displacement position L4 of the focus lens, out of the two ends of the movable range, and to actually move the focus lens. 19 is controlled.

  In the case where the corresponding curve between the focus position and the autofocus evaluation value is defined as shown in FIG. 5B (maximum value Lm), for example, when the CPU 15 determines that it is close, that is, the autofocus evaluation value is When the CPU 15 is at the displacement position L5 corresponding to a value larger than the threshold A (which is of course larger than the threshold B), the CPU 15 moves the focus lens at the time of the photographing start operation out of the two ends of the movable range. The motor driver 19 is controlled to move to the end L2 having the shorter distance from the displacement position L3 of the focus lens and to actually move.

  On the other hand, when it is determined that the CPU 15 is not close, that is, when the autofocus evaluation value is at the displacement position L6 corresponding to a value smaller than the threshold B (of course, smaller than the threshold A), the CPU 15 starts photographing. The motor driver is determined so as to move the focus lens during operation to the end L2 which is farther from the displacement position L6 of the focus lens, out of the two ends of the movable range. 19 is controlled.

  Thus, according to the camera according to the present embodiment, the displacement position Lm corresponding to the optimum in-focus state can be searched earlier than in the past.

  In addition, the search operation for the displacement position Lm corresponding to the optimal focus state does not set the search range to a range narrower than the movable range (L1 to L2) of the focus lens from the beginning. In the meantime, the search can be completed before reaching approximately half of the movable range.

  Note that there is a difference in focal depth depending on the focal length of the photographing lens system 1, and the characteristic of the autofocus evaluation value (characteristic with respect to the displacement position) varies depending on the difference in focal depth. , B can be set to optimum values corresponding to the focal length of the taking lens system 1.

  Further, it is preferable to set the aperture to the full aperture before the shutter release button is pressed (before the shooting start operation). This is because by opening, the depth of focus is reduced, the range in which the AF evaluation value can be output is limited, and the subject distance can be predicted with higher accuracy.

  Furthermore, in the macro shooting mode for shooting a subject at a close distance, when the shooting lens system 1 is a zoom optical system, macro shooting using the telephoto end side and macro shooting using the wide angle end side are as follows: Since a large difference occurs in the focus position, it is preferable to set the displacement characteristics based on the correspondence between the focus pulse (number of pulses of the pulse motor) and the imaging range, as shown in FIG.

  In the above-described embodiment, the motor driver 19 (motor) as the driving unit, the digital signal processing IC 32 including the CPU 15 as the evaluation value calculation unit, the operation unit 20 as the photographing start operation input unit, and the control unit The digital signal processing IC 32 corresponds to an embodiment of the autofocus control device of the present invention.

  Here, FIG. 6 is a graph of the focus extension amount with respect to the subject distance (1 / L) at a typical focal length. As can be seen from this graph, the focus feed amount increases as the focal length increases. Accordingly, the operation time for performing the autofocus is also increased.

  In particular, the difference becomes even greater in macro photography at close range. When macro shooting is performed at a long focal length, the autofocus operation can be started from an end point closer to the subject distance, so that the effect of shortening the time required for the autofocus operation can be further increased.

  In the above-described embodiment, the threshold value to be compared with the autofocus evaluation value is set as two threshold values A and B. However, the autofocus control device and the autofocus according to the present invention are set. In the control method and the image forming apparatus, the number of threshold values is not limited to two, and the number of threshold values may be one. Similar actions and effects can be achieved.

1 is a block diagram showing an overview of the overall system configuration of a digital still camera as an embodiment of an autofocus control device, an autofocus control method, and an image forming apparatus according to the present invention. It is a top view which shows typically the external appearance structure of the camera shown in FIG. It is a front view which shows typically the external appearance structure of the camera shown in FIG. It is a rear view which shows typically the external appearance structure of the camera shown in FIG. It is a graph which shows the correspondence of a focus position and an auto-focus evaluation value. It is a graph which shows the correspondence of a macro imaging | photography range and the number of focus pulses.

Explanation of symbols

A Threshold B Threshold L1, L2 Both ends L3, L4 of the movable range of the focus optical system Displacement position Lm of the focus optical system immediately before the photographing start operation is input Displacement position corresponding to the optimum focus state

Claims (8)

Drive means for displacing at least one of the focus optical system and an imaging device that captures an image projected through the focus optical system within the movable range;
Evaluation value calculation means for calculating an autofocus evaluation value representing the degree of focus of the image in the imaging device, based on image data obtained corresponding to the image projected on the imaging device;
A shooting start operation input means for inputting a shooting start operation;
When the shooting start operation is input to the shooting start operation input unit, after moving at least one of the focus optical system and the imaging device to one end of the movable range, The evaluation value calculating means calculates the autofocus evaluation value at every predetermined timing during the displacement while controlling the driving means to be displaced from the end portion toward the other end portion. controls, e Bei and control means for searching for the displacement position corresponding to the best-fit focus condition of the image based on the auto-focus evaluation value obtained,
Wherein, prior to the input of the start of photographing operation to the photographing start operation input means, the acquired auto focus evaluation value, and the acquired auto focus evaluation value and the pre-Me set predetermined threshold the comparison was performed at predetermined time intervals, when the operation of the photographing start has been made, based on the results of the comparisons at the time the operation is input to the photographing start, the auto-focus evaluation value is the predetermined When it is larger than the threshold value , an end portion having a shorter moving distance is selected from the two end portions of the movable range , and when the autofocus evaluation value is not larger than the predetermined threshold value, the movable range is selected. An autofocus control device that selects an end of the two ends that is not short in moving distance . The autofocus control apparatus according to claim 1, wherein the threshold value is changed according to a focal length of the focus optical system. The control means controls the aperture diameter for limiting the light beam passing through the focus optical system to be maximum on the open side when obtaining the autofocus evaluation value prior to the photographing start operation. The autofocus control device according to claim 1 or 2 . An image forming apparatus comprising the automatic focusing control apparatus according to any one of claims 1 or et 3. After moving at least one of the focus optical system and the imaging device that outputs image data corresponding to the image projected through the focus optical system to either end of the movable range, from the end An autofocus evaluation value that represents the degree of focus of the image in the imaging device based on the image data at each predetermined timing during the displacement period while controlling to be displaced toward the other end. In the autofocus control method of controlling to calculate, and searching for the displacement position corresponding to the optimal focus state of the image based on each obtained autofocus evaluation value,
Standing earlier photographing start operation, the acquired auto focus evaluation value is compared with the acquired auto focus evaluation value and the pre-Me set predetermined threshold and performed at predetermined time intervals, the imaging start operation is row when the cracks, based on the results of the comparisons at the time of the photographing start operation has been performed, when said auto-focus evaluation value is greater than the predetermined threshold value, of the two ends of the movable range When the end portion with the shorter moving distance is selected and the autofocus evaluation value is not larger than the predetermined threshold value, the end portion with the shorter moving distance of the two end portions of the movable range is selected. An autofocus control method characterized by selecting. 6. The autofocus control method according to claim 5 , wherein the threshold value is changed in accordance with a focal length of the focus optical system. 7. The autofocus control method according to claim 5 , wherein, when the autofocus evaluation value is obtained prior to the photographing start operation, an aperture diameter for limiting a light beam passing through the lens is set to an open state. . A macro autofocus control method to which a macro shooting mode for shooting a subject at a close distance is applied, wherein the autofocus control method according to any one of claims 5 to 7 is applied. Autofocus control method.

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