JP2010122410A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an imaging apparatus and an imaging method that eliminate deviation between a set AF area and an actual AF area when performing climbing AF while performing exposure by a rolling shutter. <P>SOLUTION: The imaging apparatus includes: a focus optical system 7-2; an imaging means 101 acquiring image data corresponding to a subject image; an AF evaluated value acquiring means acquiring an AF evaluated value from the data corresponding to at least one AF area in the image data when acquiring the image data while moving the focus optical system during exposure by the imaging means; and a focusing position detection means detecting a focusing position by using the AF evaluated value obtained by the AF evaluated value acquiring means while moving the focus optical system 7-2 within a focus driving range, and further includes: a correction means for correcting correspondence relation between the position of the focus optical system 7-2 and the AF evaluated value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an imaging method such as a digital camera, a mobile phone with a camera, and a portable information device having an imaging function such as a PDA, and particularly suitable for an imaging apparatus equipped with a CMOS image sensor. It is.

  In addition to an electronic imaging device such as a digital still camera, an imaging device generally includes an autofocus (hereinafter referred to as “AF”) device that automatically focuses on a subject. It is. As an AF control method in the AF apparatus, for example, hill-climbing AF control as described in Patent Document 1 is widely used. In this hill-climbing AF control, an integrated value of the luminance difference between adjacent pixels is obtained from the video signal output from the image sensor, and this integrated value of the luminance difference is used as an AF evaluation value indicating the degree of focusing. When the subject is in focus, the outline of the subject is clear and the luminance difference between adjacent pixels increases, so the AF evaluation value increases. In the out-of-focus state, the contour portion of the subject is blurred, so the luminance difference between the pixels is small and the AF evaluation value is small. When the AF operation is executed, such an AF evaluation value is sequentially acquired while moving a focusing lens that is configured as at least a part of the imaging lens, and the AF evaluation value is maximized, that is, AF The peak position of the evaluation value is detected as a focal point, and the focusing lens is positioned at this focal point and stopped.

  In recent years, in order to cope with the downsizing of digital still cameras, the downsizing of the image sensor has progressed, and there are also those using a CMOS (Complementary Metal Oxide Semiconductor) image sensor instead of the CCD (Charge Coupled Device) image sensor that has been widely used conventionally. It has increased. A CMOS image sensor is slightly larger in size than a CCD image sensor, but has an advantage that imaging speed can be increased, power can be saved, and high integration can be achieved.

  When using a CMOS image sensor, exposure is performed using a mechanical shutter in the same way as a CCD image sensor when taking a still image. However, when a captured image is monitored in real time, exposure is performed using a rolling shutter that uses only an electronic shutter. I do.

  FIG. 16 is a capture timing chart when an image is captured by the rolling shutter. In addition to controlling the exposure time, the rolling shutter outputs an image signal while performing exposure, so that the exposure time (timing) differs between the upper surface and the lower surface of one image. Therefore, for example, as shown in FIG. 19A, when a square object moving horizontally is imaged and monitored, the image displayed on the display is a parallelogram as shown in FIG. 19B. Distorted into a shape. Incidentally, in the case of a CCD image sensor, since all pixels are exposed simultaneously, and signals corresponding to the charges accumulated for each pixel are sequentially transferred by exposure, image distortion as in the case of using a CMOS image sensor does not occur.

  Therefore, when performing hill-climbing AF while performing exposure with a rolling shutter, the focus position must be corrected. For example, when the focus lens is driven by a pulse motor and the pulse motor is driven by 4 pulses during exposure of one image, the focus area is on the time axis in one image as shown in FIG. In this case, the exposure is performed in a state shifted by the above four pulses at the maximum. Therefore, when there are a plurality of areas used for AF, the focus position must be corrected. Further, since the lower part of one image always outputs an image after outputting four pulses for driving the focus lens, the focus driving amount is reduced by four pulses compared to the upper part of one image. Therefore, considering the focus drive amount, it is necessary to perform exposure in a state where the lower part of one image is further driven by four pulses compared to the upper part (see FIG. 22).

  The problem of deviation of the evaluation value due to the deviation of the AF area position will be further described with reference to FIGS. Here, consider a case where AF is performed on a planar subject. As shown in FIG. 20, when the AF area is set at the top, middle, and bottom of the screen, the AF evaluation value is acquired by exposure using the rolling shutter while the focus lens is driven. The result is shown in FIG. Curves indicated by circled numbers 1, 2, and 3 in FIG. 21 indicate AF evaluation values in the upper, middle, and lower AF areas shown in FIG. 20, respectively. Even in the case of a flat subject, as shown in FIG. 21, the peak of the curve indicating the AF evaluation value is greatly shifted on the time axis. Further, due to the characteristics of the rolling shutter, the shift amount of the peak position of the AF evaluation value increases on the time axis as the AF area becomes a lower position on the screen. Since the focus optical system is driven by a pulse output during this peak position shift, the peak position shift becomes a focus position shift. Therefore, it is necessary to correct this.

  As a known technique related to the present invention, there is an imaging system described in Patent Document 2. This is because, in a camera with interchangeable lenses, the focus lens passes through each position and the history information of each position of the focus lens in consideration of the delay in transmission of focus lens position information from the interchangeable lens to the camera. By recording the time-series lens position history information associated with the time information at the time point in the memory in the interchangeable lens, and by specifying the in-focus position of the focus lens with reference to the time-series lens position history information, This is intended to improve AF accuracy. However, the invention described in Patent Document 2 does not consider the shift of the focus position due to the partial delay of the image signal in one imaging screen by the rolling shutter using the CMOS imaging element. Therefore, the position of the focus lens is controlled to a position deviated from the original in-focus position, and satisfactory AF accuracy may not be obtained. Therefore, it is desired to develop a technique that corrects a partial delay of an image signal in one imaging screen.

  Further, Patent Document 3 describes an imaging apparatus that improves AF accuracy by providing a mode in which the position and size of an AF detection value detection area can be changed according to the subject. . However, the invention described in Patent Document 3 is also processed when the AF area is made variable so that the focus position in the screen shifts and the focus lens position shifts from the original focus position. In some cases, satisfactory AF accuracy could not be obtained.

Japanese Examined Patent Publication No. 39-5265 JP 2008-175886 A JP 2008-052022 A

  In the present invention, when performing hill-climbing AF while exposing with a rolling shutter, the AF in-focus position is shifted and set according to the exposure time of the rolling shutter in order to solve the above-described problems of the prior art. It is an object of the present invention to provide an imaging apparatus and an imaging method that can eliminate a shift between an AF area and an actual AF area.

  It is another object of the present invention to provide an imaging apparatus and an imaging method capable of expanding a focus driving range by a predetermined driving step and preventing a decrease in AF accuracy at a limit position of the focus driving range.

  The present invention provides a focus optical system, an imaging unit that acquires image data corresponding to a subject image, and the image data when acquiring the image data while moving the focus optical system during exposure by the imaging unit. AF evaluation value acquisition means for acquiring an AF evaluation value from data corresponding to at least one AF area, and the AF evaluation value acquired by the AF evaluation value acquisition means while moving the focus optical system within a focus drive range A focus position detecting means for detecting a focus position using the evaluation value, and further comprising a correction means for correcting the correspondence between the position of the focus optical system and the AF evaluation value. Features.

The correction unit may be configured to correct the correspondence relationship between the position of the focus optical system and the AF evaluation value based on a correction amount corresponding to an exposure time by the imaging unit for each AF area.
The correction unit may be configured to change the correction amount based on an area where the AF area is located on a screen on which the image data is displayed.
The correction means may be configured to increase the correction amount as the AF area is located in a lower area on the screen on which the image data is displayed.
The focus position detecting means may be configured to expand the focus drive range by a predetermined drive step and detect the focus position within the widened focus drive range.

  According to the present invention, the imaging device includes the focus position detection unit that detects the focus position using the AF evaluation value acquired by the AF evaluation value acquisition unit while moving the focus optical system within the focus drive range. The apparatus includes a correction unit that corrects the correspondence between the position of the focus optical system and the AF evaluation value, thereby correcting the shift of the in-focus position due to the difference in the focus area in one image, thereby improving the AF accuracy. Can be increased.

Hereinafter, embodiments of an imaging apparatus and an imaging method according to the present invention will be described with reference to the drawings.
2, 3 and 4 are external views showing an example of a digital still camera which is an example of an imaging apparatus according to the present invention. FIG. 1 is a block diagram showing an outline of a system configuration example inside a digital still camera as shown in FIGS.

  2 to 4, a release switch SW1, a mode dial SW2, and a sub liquid crystal display (hereinafter referred to as “LCD”) 1 are arranged on the upper surface of the camera. In front of the camera, a lens barrel unit 7 including a photographing lens, an objective side of the optical viewfinder 4, a strobe light emitting unit 3, a distance measuring unit 5, a remote control light receiving unit 6, a memory card loading chamber and a battery loading chamber lid 2 are arranged. Has been. On the back of the camera, a power switch 13, LCD monitor 10, AF LED 8, strobe LED 9, eyepiece of optical viewfinder 4, wide-angle direction zoom switch SW3, telephoto direction zoom switch SW4, self-timer setting and release switch SW5, Menu switch SW6, upward movement and strobe set switch SW7, right movement switch SW8, display switch SW9, downward movement and macro switch SW10, left movement and image confirmation switch SW11, OK switch SW12, and quick access switch SW13 are arranged.

  The system configuration inside the digital still camera is as follows. In FIG. 1, each part of the digital still camera is configured to be controlled by a digital still camera processor 104 (hereinafter simply referred to as “processor 104”). The processor 104 includes a CMOS1 signal processing block 104-1, a CMOS2 signal processing block 104-2, a CPU block 104-3, a local SRAM 104-4, a USB block 104-5, a serial block 104-6, and a JPEG / CODEC block 104-7. , A RESIZE block 104-8, a TV signal display block 104-9, and a memory card controller block 104-10, which are connected to each other via a bus line. An SDRAM 103 that stores RAW-RGB image data, YUV image data, and JPEG image data is disposed outside the processor 104 and is connected to the processor 104 by a bus line. A RAM 107, a built-in memory 120, and a ROM 108 storing a control program are also arranged outside the processor 104, and are connected to the processor 104 by a bus line.

  The lens barrel unit 7 includes a zoom optical system 7-1 having a zoom lens 7-1a, a focus optical system 7-2 having a focus lens 7-2a, an aperture unit 7-3 having an aperture 7-3a, and a mechanism shutter 7. -4a, mechanical shutter unit 7-4. The zoom optical system 7-1, the focus optical system 7-2, the aperture unit 7-3, and the mechanical shutter unit 7-4 are respectively a zoom motor 7-1b, a focus motor 7-2b, an aperture motor 7-3b, and a mechanical shutter motor. These motors are configured to be controlled by a motor driver 7-5 controlled by a CPU block 104-3 of the processor 104.

  The lens barrel unit 7 has a photographing lens that connects a subject image to the CMOS 101 that is an image sensor. The CMOS 101 constitutes an area sensor in which pixels are two-dimensionally arranged. The subject image is converted into an image signal and input to the F / E-IC 102. As is well known, the F / E-IC 102 includes a CDS 102-1, an ADC 102-2, and an A / D conversion unit 102-3. The image signal is subjected to predetermined processing, converted into a digital signal, and converted into a CMOS 1 of the processor 104. The signal is input to the signal processing block 104-1. These signal processing operations are controlled via the TG 102-4 by the vertical drive signal VD and the horizontal drive signal HD output from the CMOS1 signal processing block 104-1 of the processor 104.

  The CPU block 104-3 of the processor 104 controls the sound recording operation by the sound recording circuit 115-1. The audio recording circuit 115-1 records the amplified signal of the audio signal converted by the microphone 115-3 by the microphone amplifier 115-2 according to the command. The CPU block 104-3 also controls the operation of the audio reproduction circuit 116-1. The audio reproduction circuit 116-1 is configured to reproduce an audio signal recorded in an appropriate memory according to a command, input the audio signal to the audio amplifier 116-2, and output the audio from the speaker 116-3. The CPU block 104-3 also emits illumination light from the strobe light emitting unit 3 by controlling the operation of the strobe circuit 114. The CPU block 104-3 controls the operation of the distance measuring unit 5.

  The CPU block 104-3 is connected to a sub CPU 109 arranged outside the processor 104, and the sub CPU 109 controls display on the sub LCD 1 via the LCD driver 111. The sub CPU 109 is further connected to an AF LED 8, a strobe LED 9, a remote control light receiving unit 6, an operation key unit including the switches SW1 to SW13, and a buzzer 113.

  The USB block 104-5 is connected to a USB connector 122, and the serial block 104-6 is connected to an RS-232C connector via a serial driver circuit 123-1. The TV display block 104-9 is connected to the LCD monitor 10 via the LCD driver 117, and is connected to the video jack 119 via the video amplifier 118. The memory card controller block 104-10 is connected to the contact of the memory card slot 121 with the card contact.

  Next, the operation of the digital still camera configured as described above will be described. Before that, the operation of the conventional digital still camera will be schematically described. By setting the mode dial SW2 shown in FIG. 1 to the recording mode, the camera is activated in the recording mode. The mode dial SW2 is set by the CPU detecting that the mode switch included in the operation unit in FIG. 2 is in the recording mode ON, and the CPU controls the motor driver 7-5 to control the lens barrel unit 7. This is done by moving it to a position where it can be photographed. Further, power is turned on to the respective parts such as the CMOS 101, the F / E-IC 102, the LCD display 10 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 the finder mode, light incident on the image sensor (CMOS 101) through the lens is converted into an electrical signal and sent to the CDS circuit 102-1 and the A / D converter 102-3 as analog R, G, and B signals. Each signal converted into a digital signal by the A / D converter 102-3 is converted into a YUV signal by the YUV conversion unit in the digital signal processing IC (SDRAM 103), and written into the frame memory by the memory controller. This YUV signal is read out to the memory controller and sent to the TV or LCD monitor 10 via the TV signal display block 104-9 to display an image. This process is performed at 1/30 second intervals, and a finder mode display updated every 1/30 seconds is obtained.

  When the release shutter button SW1 is pressed, an AF evaluation value indicating the degree of focus on the screen and an AE evaluation value indicating the exposure state are calculated from the digital RGB signal captured in the CMOS I / F block of the signal processing IC. The The AF evaluation value data is read by the microcomputer as feature data and used for AF processing. When the integral value is in a focused state, the edge portion of the subject is clear, so that the high frequency component is the highest. By utilizing this, during the focus detection operation by AF, the AF evaluation value at each focus lens position is acquired, and the point (peak position) at which the maximum is obtained is detected. Considering the fact that there are multiple points that are maximal, if there are multiple points, determine the magnitude of the evaluation value of the peak position, the degree of decrease and increase of the evaluation values around it, and combine the points with reliability. AF is executed as a focal position candidate. Such focus detection by AF is executed in the processor 104 centering on the CPU block 104-3. Further, the motor driver 7-5 is driven by a command from the CPU block 104-3, and focusing is performed by driving the focus optical system 7-2 by the motor driver 7-5. Details of the AF control will be described in the following embodiments.

  The AF evaluation value can be calculated from any range of the digital RGB signals in the screen. The AF area is performed in a plurality of areas or a single area depending on the AF mode. The mode can be switched between the single AF mode and the multi AF mode by the mode dial SW2. For example, when the single AF mode is selected, as shown in FIG. 9, one area near the center in the finder (in this embodiment, 40% in the horizontal direction and 30% in the vertical direction) is an AF area. And When the multi-AF mode is selected, as shown in FIG. 10, five areas of 20% in the horizontal direction × 20% in the vertical direction are set as the AF areas.

  Next, as the AE evaluation value, the digital RGB signal is divided into several areas (the same as the AF area in this digital camera) as shown in FIG. 15, and the luminance data in the area is used. In each AE area, pixels exceeding a predetermined threshold among the pixels in each area are set as target pixels, and their luminance values are added and multiplied by the number of target pixels to obtain an AE evaluation value. An appropriate exposure amount is calculated from the luminance distribution of each area, and the exposure amount is corrected for the next frame to be captured.

  The operation of the digital camera according to the first embodiment will be described. FIG. 5 shows an overall flow regarding the AF control. The operation steps are expressed as “5-1”, “5-2”,. When the power is turned on, the camera first enters a finder mode state as shown in FIG. Next, AF area setting processing is performed in this state (5-1). The AF area is determined by the AF mode. That is, the state of the mode dial SW2 is confirmed, and it is confirmed whether the AF mode is the single AF mode or the multi AF mode. In the case of the multi AF mode, the multi area is set and the finder mode is set to the multi AF mode as shown in FIG. In the case of the single AF mode, the single area is set and the finder mode is set to the single AF mode as shown in FIG.

  Next, it is confirmed whether or not the release SW1 has been pressed (5-2). When release SW1 is pressed, the following processing is performed. First, a focus optical system such as a focus lens is driven to move to a focus operation start position (5-3). In this embodiment, the closest position is set as the focus operation start position. The closest position varies depending on the optical system, but generally around 30 cm is preferable. Next, by the lens driving process (5-4), the focus optical system is driven to an infinite position at a certain interval or step (5-6). In this embodiment, a pulse motor is used as the focus motor 7-2b, and an in-focus distance of 30 cm to infinity is driven in units of 4 pulses per exposure screen (for example, 1/30 second). . In parallel with the driving of the focus optical system, an AF evaluation value for the AF area is acquired by AF evaluation value acquisition processing (5-5). The above operation is performed until the focus position reaches infinity.

  Next, area selection processing (5-7) is performed. This part is a characteristic part of the present invention. This area selection processing (5-7) is performed according to the procedure shown in FIG. In FIG. 6, first, focus determination processing (6-1) is performed from the acquired AF evaluation value for each AF area. Here, the reliability of the AF evaluation value is evaluated, and the peak position in the evaluation value is determined. In the reliability evaluation, for example, a peak position having an evaluation value equal to or greater than a predetermined value, or a peak position whose descending or rising degree with respect to surrounding evaluation values is equal to or greater than a predetermined value is set as a reliable peak position. Next, as a result of this determination, it is determined whether there is a reliable peak position (6-2). If there is a reliable peak position, correction shift processing is performed for that area (6-3). When performing the correction shift process, it is first determined which area is the focused area.

The area determination is determined by dividing the area into upper, middle, and lower three areas as shown in FIG. 12 and which of the three areas the AF area is included in. Table 1 is a correspondence table regarding the selection of the area. The area numbers are from 1 to 5 in accordance with FIG. 10, and the shift areas are three areas 1, 2, and 3 as shown in FIG. In this embodiment, the region 2 is determined in the single AF mode. In the multi AF mode, as is clear from FIG. 10, the area number “1” is determined as the area 1, the area numbers “2”, “3”, and “4” are determined as the area 2, and the area number “5” is determined as the area 3. .
Table 1

Table 2 shows the correspondence of the shift amount to the exposure amount (Tv). Referring to the timing chart of FIG. 17, considering the case of Tv5 (33 ms), the exposure of the upper half of one screen is performed while the focus optical system is driven by the previous four pulses. However, the lower half of the exposure is performed while being driven with the subsequent four pulses. Since the upper and lower surfaces are exposed while driving the focusing optical system for 4 pulses, the AF evaluation value that is actually output is obtained by shifting to the average position of the 4 pulses. That is, the upper half of the exposure is shifted before and after the second pulse, and the lower half of the exposure is shifted before and after the sixth pulse, and the evaluation values at these positions are obtained. In the present invention, the shift amount is calculated based on the vertical drive signal VD. As shown in Table 2, when the exposure amount is Tv5, the shift amount in area 1 is “2”, the shift amount in area 2 is “4”, and the shift amount in area 3 is “6”. Is set. Further, in the case of driving in the electronic shutter such as Tv6 and 7, since it is necessary to increase the shift amount by the already driven pulse, the shift amount is larger in the electronic shutter than in the case of Tv5. The drive pulse is taken into account.
Table 2

  Correction is performed by the above-described correction shift process for each in-focus area, and in the state where this correction has been performed, next, determination processing (6-5) for an area having a peak position is performed. Regarding the area determination, all in-focus areas are targeted, and those that show a peak at a closer distance are set as in-focus positions. In the determination step of whether or not there is a reliable peak position, that is, in the determination step of presence or absence of the in-focus area (6-2), if no in-focus area with a peak is found, it is determined as NG (6-4) As shown in FIG. 14, the AF frame in the single AF mode is displayed.

Returning to FIG. 5, when the area selection process (5-7) is completed, an area display process is performed (5-8). In the area display process, an area portion corresponding to the area selected in the area selection process (5-7) is displayed. FIG. 13 shows an example of AF area display when a person is a subject. Finally, in the focus position movement process step (5-9), the focus optical system is moved to the focus position (focus position) corresponding to the area selected in the area selection process (5-7). When it is determined as NG in the area selection process (5-7) (when the in-focus area is not found in FIG. 6), the focus optical system is moved to the focus position corresponding to the NG distance. In general, the NG distance may use a hyperfocal distance, but in the example of the digital camera to which the present invention is applied, the NG distance is set to 2.5 m, and the focus optical system is set so as to focus on an object 2.5 m away Is supposed to move.
The AF operation described above is executed by the digital still camera processor 104 operating according to a control program stored in the ROM 108 and issuing an operation command to each unit.

  By the above processing, the correspondence between the position of the focus optical system and the acquired AF evaluation value is shifted, and the correspondence between the position of the focus optical system generated by the rolling shutter using the CMOS image sensor and the acquired AF evaluation value. The in-focus position can be obtained with high accuracy. Then, the actual photographing / recording can be performed at the obtained in-focus position.

  Next, the operation of the digital camera according to the second embodiment will be described. FIG. 7 shows an overall flow relating to AF in the second embodiment. First, when the camera is turned on, a finder mode as shown in FIG. 13 is set. Subsequently, AF area setting processing is performed (7-1). The AF area is determined by the AF mode. The state of the mode dial SW2 is confirmed, and it is confirmed whether the AF mode is the single AF mode or the multi AF mode. In the case of the multi AF mode, the multi area is set, and the finder mode is set to a mode for displaying a plurality of AF areas as shown in FIG. 10, for example. In the case of the single AF mode, the single area is set, and the finder mode is set to a mode in which one AF area is displayed at substantially the center of the screen as shown in FIG.

  Next, it is confirmed whether or not the release SW1 has been pressed (7-2). When release SW1 is pressed, the following processing is performed. First, an AF drive range determination process for determining a focus drive range during AF is performed (7-3). A specific example of this processing is shown in FIG. In FIG. 8, first, it is confirmed whether or not the focal length is in a wide angle (Wide) range (8-1). If it is in the wide-angle range, the focus step pulse during one exposure is set to four pulses (8-2). Otherwise, it is determined that the focal length is on the telephoto side (Tele), and one exposure is being performed. The focus step pulse is set to 8 pulses (8-3). Next, the margin amount to be added to the focus drive amount is set from the focus step pulse set as described above (8-4).

  The reason why such a margin is required is as follows. When exposure is performed with the rolling shutter, as shown in FIG. 18, since the lower surface with respect to the upper surface of the screen is output after the focus drive for the next exposure (exposure 2) starts, the start of exposure is actually output during one exposure. Delayed by the focus step. FIG. 22 shows a problem caused by this. Normally, if the focus optical system is focused on infinity, it is not necessary to drive the focus optical system any more, so that the drive of the focus optical system ends at the infinity position (see FIG. 22A). However, when the upper part of the screen is exposed while driving the focus optical system near infinity and reaches the infinity position, the lower part of the screen is exposed without driving the focus optical system. For this reason, the upper screen is exposed and the image signal is transferred while driving the focus optical system, while the lower screen is exposed and the image signal is transferred with the focus optical system being driven. Will be. As a result, as shown in FIG. 22B, for example, when the subject is a person, the focus optical system is driven and not driven in the vicinity of the most important person's face. It will be mixed, and there is a risk of reducing the accuracy of AF.

In order to avoid such inconvenience, as described above, a margin amount to be added to the predetermined focus drive amount is set so that the drive continues even if the focus optical system reaches the infinity position. Since the same occurs at the drive start position of the focus optical system, a margin amount to be added to the focus drive amount is also set on the drive start position side. Table 3 is a correspondence table of pulse drive margins. The number of pulses for one focus step is added to the far side (infinity) for the near side and set. The drive step can be set as appropriate, for example, 2 pulses, 4 pulses, 8 pulses, and the same number of pulses as the set number of pulses is set as a margin amount to be added to the focus drive amount.
Table 3

The correspondence of the shift amount with respect to the exposure amount (Tv) is shown in Table 4. When the drive step of the focus optical system during one exposure is 4 pulses and 8 pulses, the shift amount is set as shown in Table 4 for each of the regions 1, 2 and 3 set in the vertical direction of the screen. ing.
Table 4

  Next, returning to FIG. 7, the focus optical system is moved to the focus drive start position (7-4). Here, the closest position is set as the focus operation start position. Although the close position may vary depending on the optical system, generally around 30 cm is preferable. Next, the focus optical system is driven to an infinite position at a certain interval by lens drive processing (7-5). Here, since the focus motor 7-2b uses a pulse motor, it is driven from 30 cm to infinity for each exposure with 4 pulses for Wide and 8 pulses for Tele. At this time, an AF evaluation value for the AF area is acquired by AF evaluation value acquisition processing (7-6) while driving the focus optical system. The above operation steps 7-5 to 7-7 are repeated until the focus position reaches infinity.

  Next, area selection processing (7-8) is performed. This area selection processing (7-8) is the same as the operation shown in FIG. That is, in FIG. 6, first, focus determination processing (6-1) is performed from the AF evaluation values for the acquired AF areas. Here, the reliability of the AF evaluation value is evaluated, and the peak position in the evaluation value is determined. Next, as a result of this determination, it is determined whether there is a reliable peak position (6-2). In the reliability evaluation, for example, a peak position having an evaluation value equal to or greater than a predetermined value, or a peak position whose descending or rising degree with respect to surrounding evaluation values is equal to or greater than a predetermined value is set as a reliable peak position. If there is a reliable peak position, correction shift processing is performed for that area (6-3). When performing the correction shift process, it is first determined which area is the focused area.

  The area determination is determined by dividing the area into three in the vertical direction as shown in FIG. 12 and which of the three areas the AF area is included in. Table 1 is a correspondence table regarding the selection of the area. The area number is from 1 to 5, and the shift area has three areas 1, 2 and 3 as shown in FIG. In the case of the single AF mode, the region 2 is determined here. In the multi AF mode, as is clear from FIG. 10, the area number “1” is determined as the area 1, the area numbers “2”, “3”, and “4” are determined as the area 2, and the area number “5” is determined as the area 3. .

  Correction is performed by the above-described correction shift process for each in-focus area, and in the state where this correction has been performed, next, determination processing (6-5) for an area having a peak position is performed. Regarding the area determination, all in-focus areas are targeted, and those that show a peak at a closer distance are set as in-focus positions. In step (6-2) for determining whether or not there is a reliable peak position, if an in-focus area with a peak is not found, it is determined as NG (6-4), and as shown in FIG. The AF frame in single AF mode is displayed.

  Returning to FIG. 7, when the area selection process (7-8) is completed, an area display process is performed (7-9). In the area display process, an area portion corresponding to the area selected in the area selection process (7-8) is displayed. FIG. 13 shows an AF area display state when a person is a subject. Whether or not there is a reliable peak position, that is, when a focused area with a peak is not found in the focused area presence / absence determination step (6-2), it is determined as NG (6-4), and FIG. As shown, the AF frame in the single AF mode is displayed.

Finally, in the focus position movement process step (5-9), the focus optical system is moved to the focus position (focus position) corresponding to the area selected in the area selection process (5-7). When it is determined as NG in the area selection process (5-7) (when the in-focus area is not found in FIG. 6), the focus optical system is moved to the focus position corresponding to the NG distance. In general, the NG distance may use a hyperfocal distance, but in the example of the digital camera to which the present invention is applied, the NG distance is set to 2.5 m, and the focus optical system is set so as to focus on an object 2.5 m away Is supposed to move.
The AF operation described above is executed by the digital still camera processor 104 operating according to a control program stored in the ROM 108 and issuing an operation command to each unit.

  With the above processing, when the focus drive range is expanded by a predetermined drive step and the AF evaluation value is acquired within the expanded focus drive range, the environment during exposure does not change, and thus a highly accurate AF evaluation value can be obtained. it can. Then, by correcting the correspondence between the obtained AF evaluation value and the position of the focus optical system and detecting the focus position, the detection accuracy of the focus position can be increased.

  In the first and second embodiments, five areas are set in the multi AF mode. However, the present invention is not limited to this, and the area may be expanded to a wider range or the number of areas may be increased. In that case, it is necessary to perform correction in a subdivided area instead of the three areas as shown in FIG.

  In the second embodiment, the setting of the number of step pulses is determined based on the focal length. However, the AF driving range, for example, a normal imaging region (for example, 30 cm to ∞) and a macro imaging region (for example, 1 cm to 30 cm) are used. If it is possible to switch at this point, more accurate AF can be realized.

1 is a block diagram illustrating a system configuration example of a digital still camera that is an embodiment of an imaging apparatus according to the present invention. It is a front view which shows the external appearance of the said digital still camera. It is a top view of the said digital still camera. It is a rear view of the digital still camera. 3 is a flowchart showing the operation of the first embodiment of the imaging apparatus according to the present invention. It is a flowchart which shows the area selection process in operation | movement of the said 1st Example. It is a flowchart which shows operation | movement of 2nd Example of the imaging device concerning this invention. It is a flowchart which shows the AF drive range determination process in operation | movement of the said 2nd Example. FIG. 10 is a field diagram showing an example of an AF area set when a single AF mode is selected in an embodiment of the present invention. FIG. 10 is a view showing an example of an AF area set when a multi AF mode is selected in an embodiment of the present invention. It is a visual field figure which shows the example of a display at the time of the finder mode in the Example of this invention. It is a visual field figure which shows the example of a division of the focusing area in this invention. FIG. 6 is a view of a field of view showing an AF area display example when a person is a subject in the present invention. It is a visual field figure which shows the example of the AF frame at the time of the single AF mode in this invention. It is a figure which shows the example which divided | segmented the digital RGB signal for acquiring AE evaluation value into an appropriate number of photometry areas. It is an acquisition timing chart in the case of acquiring an image with a rolling shutter. 5 is a timing chart showing that the focus timing differs between the upper half exposure and the lower half exposure of one screen in the above image capture. Similarly, the lower surface with respect to the upper surface of the screen is a timing chart showing that the focus drive for the next exposure is output after starting. The problems of the rolling shutter are shown, in which (a) is a field diagram showing an example of a moving subject, and (b) is a field diagram showing an example in which the subject is displayed distorted. It is a figure for demonstrating the problem of a rolling shutter, Comprising: It is a visual field figure which shows the example in which the focus area is set in three places up and down. It is a graph which shows a mode that the peak of the curve which shows AF evaluation value shifts | deviates on a time axis in the said three focus areas. This shows a problem with the rolling shutter. (A) is a timing chart showing that the upper surface of the screen and the lower surface are output after the focus drive for the next exposure is started, and (b) is the focus position generated thereby. It is a visual field diagram for demonstrating the shift | offset | difference of.

Explanation of symbols

7-2 Focus optical system 101 CMOS as imaging means

Claims (10)

Focus optics,
Imaging means for acquiring image data corresponding to the subject image;
AF evaluation value acquisition means for acquiring an AF evaluation value from data corresponding to at least one AF area in the image data when acquiring the image data while moving the focus optical system during exposure by the imaging means; ,
A focus position detection unit that detects a focus position using the AF evaluation value acquired by the AF evaluation value acquisition unit while moving the focus optical system within a focus drive range, and
An imaging apparatus, further comprising a correction unit that corrects a correspondence relationship between the position of the focus optical system and the AF evaluation value.   The correction means corrects the correspondence between the position of the focus optical system and the AF evaluation value based on a correction amount according to an exposure time by the imaging means for each AF area. The imaging device described.   The imaging apparatus according to claim 2, wherein the correction unit changes the correction amount based on an area where the AF area is located on a screen on which the image data is displayed.   The imaging apparatus according to claim 3, wherein the correction unit increases the correction amount as the AF area is located in a lower area on a screen on which the image data is displayed.   5. The focus position detection unit according to claim 1, wherein the focus position detection unit expands the focus drive range by a predetermined drive step and detects the focus position within the expanded focus drive range. Imaging device. Obtain image data corresponding to the subject image by the imaging means,
When acquiring the image data while moving a focus optical system during exposure by the imaging unit, an AF evaluation value is acquired from data corresponding to at least one AF area in the image data;
An imaging method for detecting an in-focus position using the AF evaluation value while moving a focus optical system within a focus drive range,
An imaging method, wherein a correspondence relationship between the position of the focus optical system and the AF evaluation value is corrected.   7. The imaging method according to claim 6, wherein the correction of the correspondence relationship between the position of the focus optical system and the AF evaluation value is performed for each AF area based on a correction amount according to an exposure time by the imaging unit.   8. The imaging method according to claim 7, wherein the correction amount of the correspondence relationship between the position of the focus optical system and the AF evaluation value is changed based on an area where the AF area is located on a screen on which image data is displayed. .   9. The correction amount of the correspondence relationship between the position of the focus optical system and the AF evaluation value is increased as the AF area is positioned in a lower area on the screen on which image data is displayed. Imaging method.   The imaging method according to claim 6, wherein the focus drive range is expanded by a predetermined drive step, and the in-focus position is detected within the expanded focus drive range.

Images