JP2018185450A - Imaging apparatus and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of performing focus detection by a phase difference system with high accuracy under a flicker light source, and a control method thereof.SOLUTION: An imaging apparatus includes: an imaging device having an imaging pixel configured to output an imaging signal according to an image formed by an imaging optical system and a focus detection pixel configured to output a phase difference signal according to a plurality of images having passed through different pupil areas of the imaging optical system; a flicker detection part configured to detect a flicker according to the imaging signal; and a control part configured to control, when the flicker detection part detects a flicker, an accumulation period of the focus detection pixel independently from an accumulation period of the imaging pixel to correct a flicker of the phase difference signal.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an imaging apparatus including a focus detection pixel and a control method thereof.

  In recent years, an image sensor having pixels for focus detection has been realized. For example, Patent Document 1 describes an imaging apparatus including an imaging element in which focus detection pixels are arranged between imaging pixels. In particular, the imaging device disclosed in Patent Document 1 describes a technique for controlling the accumulation period of focus detection pixels independently of the accumulation period of imaging pixels. Thereby, the accumulation period of the focus detection pixels is adjusted so that the luminance of the phase difference signal is optimum for focus detection, and the accuracy of focus detection is improved.

JP 2010-219958 A

  On the other hand, in order to suppress flicker under a flicker light source, flicker correction is known in which the accumulation period of imaging pixels is adjusted according to the flicker frequency. However, when the accumulation period of the focus detection pixels is controlled independently of the accumulation period of the imaging pixels as in the technique described in Patent Document 1, the flicker of the imaging signal is suppressed by the flicker correction, but the phase difference signal Flicker is not corrected. As a result, the accuracy of focus detection sometimes deteriorates due to the flicker effect superimposed on the phase difference signal. SUMMARY An advantage of some aspects of the invention is that it provides an imaging apparatus capable of performing focus detection by a phase difference method with high accuracy even under a flicker light source and a control method thereof.

  According to one aspect of the present invention, an imaging pixel that outputs an imaging signal based on an image formed by an imaging optical system, and a phase difference signal based on a plurality of images that have passed through different pupil regions of the imaging optical system are output. An imaging element having a focus detection pixel, a flicker detection unit that detects flicker based on an imaging signal, and a storage period of the focus detection pixel when the flicker detection unit detects flicker. There is provided an imaging apparatus comprising: a control unit that independently controls and performs flicker correction of a phase difference signal.

  According to the present invention, it is possible to provide an imaging apparatus capable of performing focus detection by a phase difference method with high accuracy even under a flicker light source and a control method therefor.

1 is a block diagram schematically showing a configuration of an imaging apparatus according to a first embodiment. It is a figure showing roughly the composition of the image sensor in the imaging device concerning a 1st embodiment. FIG. 3 is an equivalent circuit diagram schematically illustrating a configuration of a pixel unit in the imaging apparatus according to the first embodiment. FIG. 2 is a plan view schematically showing a configuration of a pixel unit in the imaging apparatus according to the first embodiment. It is a figure which shows schematically the structure of the pixel array in the imaging device which concerns on 1st Embodiment. It is a figure which shows schematically the pupil area | region in the imaging device which concerns on 1st Embodiment. It is a figure which shows schematically the scanning method of the pixel array in the imaging device which concerns on 1st Embodiment. It is a figure which shows the example of the detection method of the flicker in the imaging device which concerns on 1st Embodiment. 3 is a flowchart illustrating a method for controlling the imaging apparatus according to the first embodiment. It is a figure which shows the example of the determination method of the amplitude of the flicker in the imaging device which concerns on 1st Embodiment. It is a 1st figure which shows the example of the setting method of the accumulation | storage period in the imaging device which concerns on 1st Embodiment. It is a 2nd figure which shows the example of the setting method of the accumulation | storage period in the imaging device which concerns on 1st Embodiment. It is a flowchart which shows the control method of the imaging device which concerns on 2nd Embodiment. It is a figure which shows the example of the setting method of the accumulation period in the imaging device which concerns on 2nd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment, In the range which does not deviate from the summary, it can change suitably. In addition, components having the same or corresponding functions in each drawing are denoted by the same reference numerals, and the description thereof may be omitted or simplified.

(First embodiment)
FIG. 1 is a block diagram schematically showing the configuration of the imaging apparatus 100 according to the first embodiment. An imaging apparatus 100 according to the present embodiment illustrated in FIG. 1 includes an imaging element 101, a flicker detection unit 102, an accumulation period calculation unit 103, an imaging element driving unit 104, and a control unit 105.

  The imaging element 101 has an imaging pixel that outputs an imaging signal based on an image formed by an imaging optical system (not shown). In addition, the image sensor 101 includes focus detection pixels that output phase difference signals based on a plurality of images that have passed through different pupil regions of the imaging optical system. Although the imaging pixel and the focus detection pixel generally have different configurations, as shown in FIGS. 3 to 4 to be described later, the imaging pixel and the focus detection pixel may have the same configuration capable of outputting both the imaging signal and the phase difference signal. Is possible.

  The flicker detection unit 102 detects the presence / absence of flicker included in the image pickup signal output from the image pickup device 101, the amplitude, the period, and the like. For example, flicker due to a fluorescent lamp occurs when fluctuations such as illumination intensity synchronized with the frequency of the commercial power supply are superimposed on the imaging signal. The accumulation period calculation unit 103 calculates drive information of the image sensor 101 for correcting flicker based on information such as the flicker amplitude and period detected by the flicker detection unit 102 and outputs the drive information to the image sensor drive unit 104. . The image sensor drive unit 104 drives the image sensor 101 according to the drive information calculated by the accumulation period calculation unit 103. The control unit 105 governs overall control of the imaging apparatus 100. Note that the storage period calculation unit 103 and the image sensor driving unit 104 may be included in the control unit 105.

  The control unit 105 according to the present embodiment can independently control the accumulation period of the imaging pixels and the accumulation period of the focus detection pixels. The accumulation period of the imaging signal is determined based on a shutter speed or the like designated in advance by the photographer. Therefore, in this way, by setting the accumulation period of the focus detection pixel to be controllable independently from the accumulation period of the imaging pixel, the focus detection pixel of the focus detection pixel can be set to have the optimum luminance of the phase difference signal for focus detection. It is possible to adjust the accumulation period.

  Next, the image sensor 101 shown in FIG. 1 will be described more specifically. FIG. 2 is a diagram schematically illustrating the configuration of the image sensor 101 in the image capturing apparatus 100 according to the first embodiment. The image sensor 101 shown in FIG. 2 includes a pixel array 201, a vertical scanning circuit 202, a readout circuit 203, a horizontal scanning circuit 204, and a serial interface 205.

  In the pixel array 201, imaging pixels and focus detection pixels are arranged in a matrix. The vertical scanning circuit 202 scans the rows of the pixel array 201 in the vertical direction. The readout circuit 203 reads out the imaging signal and the phase difference signal from the imaging pixels and focus detection pixels in the row scanned by the vertical scanning circuit 202. The readout circuit 203 includes a memory, a gain amplifier, an AD converter, and the like for reading out signals from the imaging pixels and focus detection pixels for each column. The horizontal scanning circuit 204 sequentially scans the signals of each column read by the reading circuit 203 and outputs the signals to the outside of the image sensor 101. The serial interface 205 is for determining the operation mode and the like of each circuit in the image sensor 101 from the outside of the image sensor 101.

  Note that the image sensor 101 may include, for example, a timing generator in addition to the components shown in FIG. The timing generator outputs a timing signal to the vertical scanning circuit 202, the readout circuit 203, the horizontal scanning circuit 204, and the like.

  Next, imaging pixels and focus detection pixels arranged in the pixel array 201 illustrated in FIG. 2 will be described. FIG. 3 is an equivalent circuit diagram schematically showing the configuration of the pixel unit 300 in the imaging apparatus 100 according to the first embodiment. FIG. 4 is a plan view schematically showing the configuration of the pixel unit 300 in the imaging apparatus 100 according to the first embodiment. In the following description, it is assumed that both the imaging pixel and the focus detection pixel have the configuration of the pixel unit 300 shown in FIGS. 3 and 4 and can output both the imaging signal and the phase difference signal. The form is not necessarily limited to such a configuration. The imaging pixel and the focus detection pixel may have different configurations.

  A pixel unit 300 shown in FIGS. 3 and 4 includes photoelectric conversion units 301 and 302, transfer transistors 307 and 308, a reset transistor 305, an amplification transistor 304, and a selection transistor 306. The vertical scanning circuit 202 controls the transfer transistors 307 and 308, the reset transistor 305, and the selection transistor 306 by control signals φTXA_n, φTXB_n, φRES_n, and φSEL_n, respectively. Control signals φTXA_n, φTXB_n, φRES_n, and φSEL_n are output to control lines 312, 313, 311 and 310, respectively. N of each control signal indicates a row number. For example, the control signal φTXA_n indicates that the control signal is output to the pixel unit 300 in the n-th row.

  The photoelectric conversion units 301 and 302 are, for example, photodiodes (PD: Photo Diode) formed on a semiconductor substrate, and photoelectrically convert images formed by the same microlens 401, respectively. In the following description, the photoelectric conversion unit 301 is referred to as “A pixel”, and the photoelectric conversion unit 302 is referred to as “B pixel”. A signal output from the A pixel is referred to as an “A signal”, and a signal output from the B pixel is referred to as a “B signal”. As shown in FIG. 4, the A pixel and the B pixel are arranged offset to the left and right with respect to the center of the microlens 401. As a result, the A pixel and the B pixel respectively output an A signal and a B signal based on an image that has passed through different pupil regions of the imaging optical system. It becomes possible to detect the focal point.

  The transfer transistor 307 is turned on when the control signal φTXA_n is H (high level), and is turned off when the control signal φTXA_n is L (low level). By turning on the transfer transistor 307, the signal charge generated in the A pixel is transferred to the floating diffusion region 303. Similarly, the transfer transistor 308 is turned on when the control signal φTXB_n is H (high level), and is turned off when the control signal φTXB_n is L (low level). By turning on the transfer transistor 308, the signal charge generated in the B pixel is transferred to the floating diffusion region 303. In FIG. 4, only the gate electrodes of the transfer transistors 307 and 308 are shown. The floating diffusion region 303 is connected to the gate terminal of the amplification transistor 304, constitutes a pixel amplifier, and also functions as a charge / voltage conversion unit.

  The reset transistor 305 is turned on when the control signal φRES_n is H (high level), and is turned off when the control signal φRES_n is L (low level). By turning on the reset transistor 305, the signal charge held in the floating diffusion region 303 is reset. Further, by simultaneously turning on the reset transistor 305 and the transfer transistor 307, the signal charge accumulated in the A pixel is reset. Also, the signal charge accumulated in the B pixel is reset by simultaneously turning on the reset transistor 305 and the transfer transistor 308.

  The selection transistor 306 is turned on when the control signal φSEL_n is H (high level), and is turned off when the control signal φSEL_n is L (low level). By turning on the selection transistor 306, the output of the amplification transistor 304 is output to the vertical output line 309. A constant current source (not shown) is connected to the vertical output line 309, and the constant current source (not shown) and the amplification transistor 304 constitute a source follower circuit.

  As described above, the pixel unit 300 shown in FIGS. 3 and 4 can be used as either an imaging pixel or a focus detection pixel. When the pixel unit 300 is used as an imaging pixel, an A signal and a B signal are added to generate an imaging signal. On the other hand, when the pixel unit 300 is used as a focus detection pixel, a pair of A signal and B signal is used as a phase difference signal. Note that it is also possible to omit the photoelectric conversion unit 302 in the pixel unit 300 illustrated in FIGS. 3 and 4 and use the pixel unit 300 having only one photoelectric conversion unit 301 as an imaging pixel.

  Next, the pixel array 201 illustrated in FIG. 2 will be described. FIG. 5 is a diagram schematically illustrating a configuration of the pixel array 201 in the imaging apparatus 100 according to the first embodiment. In the pixel array 201 shown in FIG. 5, the pixel units 300 shown in FIGS. 3 and 4 are arranged in a matrix. With such a configuration, a two-dimensional image can be generated using the imaging signal output from the pixel unit 300. Further, the focus of the subject image can be detected by comparing the phase difference signals output from the pixel unit 300.

  FIG. 6 is a diagram schematically showing pupil regions 607 and 608 in the imaging apparatus 100 according to the first embodiment. Light incident from the left side of FIG. 6 is collected by an imaging optical system (not shown), passes through the exit pupil 606, and proceeds to the right along the optical axis 609. Thereafter, the light beams that have passed through the microlens 401 and the color filter 603 form images on the photoelectric conversion units 301 and 302 of the pixel array 201, respectively.

  As illustrated in FIG. 6, the A pixel (photoelectric conversion unit 301) and the B pixel (photoelectric conversion unit 302) are respectively offset with respect to the center of the microlens 401. As a result, the A pixel and the B pixel respectively output the A signal and the B signal based on the images that have passed through the different pupil regions 608 and 607 of the imaging optical system, so the A signal and the B signal are compared. It becomes possible to detect the focus of the subject image. FIG. 6 shows the outermost periphery 610 of the light beam that passes through the upper pupil region 607 and forms an image on the lower B pixel, and the light beam that passes through the lower pupil region 608 and forms an image on the upper A pixel. The outermost periphery 612 is shown.

  FIG. 7 is a diagram schematically illustrating a scanning method of the pixel array 201 in the imaging apparatus 100 according to the first embodiment. FIG. 7A schematically shows the pixel array 201 shown in FIG. The hatched portions on the upper and left sides of the pixel array 201 indicate an optical black (OB) portion where the shielded pixel unit 300 is arranged. Further, the row number of the pixel array 201 is shown on the left side of FIG.

  FIG. 7B shows an example of a scanning method of the pixel array 201 shown in FIG. First, the vertical scanning circuit 202 performs a first scan for generating an image. In the first scanning, the image pickup signal obtained by adding the A signal and the B signal is sequentially read while scanning the pixel array 201 by thinning out the pixel array 201 in the vertical direction at the first cycle. Next, the vertical scanning circuit 202 performs a second scan for performing focus detection. In the second scanning, the phase difference signal that is a pair of the A signal and the B signal is sequentially read while thinning and scanning the rows of the pixel array 201 that have not been read in the first scanning in the second period. As described above, in the second scanning, the A signal and the B signal are separately read out for the same pixel unit 300, but the second scanning is a scanning in which only the A signal is read and a scanning in which only the B signal is read. It may be divided into two scans.

  Thereafter, an image is generated from the imaging signal read in the first scan, and the focus is detected by comparing the phase difference signals read in the second scan. As described above, in the reading method performed while thinning out in the vertical direction, the resolution of the generated image is reduced. Therefore, it is suitable for live view images and moving images that require fewer rows to be read compared to the still image mode. When focus detection is not performed, only the first scan is performed without thinning out all the rows of the pixel array 201.

  Next, the first scanning and the second scanning by the vertical scanning circuit 202 will be described more specifically with reference to FIG. In FIG. 7B, the rows surrounded by a thick frame are read target rows in the first scan, and the other rows are thinned out in the first scan. In addition, the row to which the vertical line pattern is added in FIG. 7B is a read target row for the second scan, and the other rows are thinned out without being read in the second scan.

  The vertical scanning circuit 202 first reads an imaging signal obtained by adding the A signal and the B signal from the pixel unit 300 arranged in the V0 row, and similarly reads the imaging signal from the V1 row to the V7 row in a cycle of 3 rows. Reading for these V0 to V7 rows is the first scan. The imaging signal read by the first scan is based on signal charges generated in both the photoelectric conversion units 301 and 302 sharing the same microlens 401. For this reason, a signal based on light incident on the entire pixel unit 300 is output as an imaging signal. Thereafter, an image is generated from the imaging signals of the V0 to V7 rows read out in the first scan.

  As described above, when reading is performed by thinning out rows in the vertical direction while reading out without thinning out columns in the horizontal direction, the number of read pixels is different between the horizontal direction and the vertical direction, and the aspect ratio of the generated image is different. End up. Therefore, the aspect ratio is converted in the subsequent processing. Alternatively, the horizontal direction may be thinned and read at the same ratio as the vertical direction, or a plurality of columns may be added and read instead of thinning.

  When the first scanning is performed up to the V7 row, the vertical scanning circuit 202 returns the scanning row to the V8 row. Then, after reading out the phase difference signal that is a pair of the A signal and the B signal from the pixel unit 300 arranged in the V8 row, the phase difference signal is similarly read out from the V9 row to the V13 row. At this time, scanning is skipped for the rows that have already been read in the first scanning. Reading for these V8 to V13 rows is the second scan. The phase difference signal read out by the second scanning is based on signal charges generated in the photoelectric conversion units 301 and 302 that share the same microlens 401. Therefore, the focus of the subject image can be detected by comparing the A signal and the B signal based on the light that has passed through different pupil regions of the imaging optical system.

  In the second scan, scanning is performed with a predetermined cycle as in the first scan, so that the readout time can be shortened and a high frame rate can be handled. In addition, when a focus detection area for performing focus detection is designated in advance by a photographer's operation or the like, it is preferable that the narrowest row range including the focus detection area is a target line for the second scan. For example, in FIG. 7B, when the focus detection area is set in the range from the V8 line to the V13 line, the second scan is performed from the V8 line to the V13 line as described above. Target row. The focus detection area may be a fixed area or may be automatically set by a known method such as subject detection.

  FIG. 7C is a diagram in which the rows scanned by the first scan and the second scan shown in FIG. 7B are rearranged in the read order. An imaging signal obtained by adding the A signal and the B signal is read out from the pixel units 300 in the V0 to V7 rows read out in the first scan. Further, a phase difference signal that is a pair of the A signal and the B signal is read out from the pixel units 300 in the V8 to V13 rows read out in the second scanning. In FIG. 7C, the A signal and the B signal read in the second scanning are separately shown as V8a and V8b, for example.

  As described above, the control unit 105 according to the present embodiment can independently control the accumulation period of the imaging pixels read by the first scan and the accumulation period of the focus detection pixels read by the second scan. The accumulation period of the imaging signal is determined based on a shutter speed or the like designated in advance by the photographer. Therefore, in this way, by setting the accumulation period of the focus detection pixel to be controllable independently from the accumulation period of the imaging pixel, the focus detection pixel of the focus detection pixel can be set to have the optimum luminance of the phase difference signal for focus detection. It is possible to adjust the accumulation period.

  FIG. 8 is a diagram illustrating an example of a flicker detection method in the imaging apparatus 100 according to the first embodiment. For example, flicker of a fluorescent lamp is generated in synchronization with the frequency of a commercial power source. The frequency of the commercial power supply is 50 Hz in eastern Japan and 60 Hz in western Japan.

  As shown in FIGS. 8A and 8B, when the period of the captured image storage period used in the live view is different from the flicker period by a half period, between frames of consecutive captured images. A flicker pattern shift occurs. For example, when the flicker cycle is 10 ms synchronized with the power supply frequency 50 Hz of the commercial power supply, the cycle of the imaging pixel accumulation period in which the pattern shift occurs is 15 ms (67 fps), 25 ms (40 fps), 35 ms (28 fps), 45 ms ( 22 fps). Here, it should be noted that the flicker cycle of 10 ms is half of the commercial power cycle of 20 ms.

  Therefore, by calculating the difference between the image in FIG. 8A and the image in FIG. 8B, it is possible to cancel the components excluding flicker in the captured image and extract only the flicker component. FIG. 8C shows a difference image calculated from the image of FIG. 8A and the image of FIG. 8B. FIG. 8D shows a signal distribution along the XY line in the vertical direction of the difference image shown in FIG. The waveform shown in FIG. 8D obtained in this manner indicates the extracted flicker noise waveform. Therefore, it is possible to detect the presence / absence of flicker, its amplitude, period, etc. based on the waveform shown in FIG.

  Since the frame rate is fixed at 30 fps or the like during live view display, flicker detection cannot be performed during live view display. Therefore, flicker detection is performed only once at the timing before the start of live view display. Further, when the period of the accumulation period of the imaging pixels used for flicker detection is 45 ms (22 fps), flicker synchronized with any commercial power source of 50 Hz or 60 Hz can be detected. Note that the flicker detection timing and flicker cycle are not necessarily limited to such values, and can be set as appropriate according to the environment.

  Hereinafter, a method for suppressing the flicker of the phase difference signal while adjusting the accumulation period of the focus detection pixel so as to obtain the luminance of the phase difference signal optimal for focus detection will be described with reference to FIGS. FIG. 9 is a flowchart illustrating a method for controlling the imaging apparatus 100 according to the first embodiment.

  In step S801, the live view is activated by a photographer's operation or the like. In step S802, the flicker detection unit 102 detects the presence / absence of flicker and the frequency thereof using the method shown in FIG.

  In step S <b> 803, the control unit 105 determines whether or not flicker is detected by the flicker detection unit 102. If flicker is detected (YES), the process proceeds to step S804, and the flicker amplitude is calculated. On the other hand, if no flicker is detected (NO), the process proceeds to step S807, the flicker correction flag is set to OFF, and the process proceeds to step S808.

  In step S805, the control unit 105 determines whether or not the calculated flicker amplitude is greater than or equal to a predetermined threshold that affects the focus detection accuracy. FIG. 10 is a diagram illustrating an example of a flicker amplitude determination method in step S805. FIG. 10A shows a case where the flicker amplitude does not affect the focus detection accuracy, and FIG. 10B shows a case where the flicker amplitude affects the focus detection accuracy.

  As shown in FIG. 10A, if the magnitude of the flicker amplitude is less than the threshold (NO), the process proceeds to step S807, the flicker correction flag is set to OFF, and the process proceeds to step S808. On the other hand, as shown in FIG. 10B, if the flicker amplitude is greater than or equal to the threshold (YES), the process proceeds to step S806, the flicker correction flag is set to ON, and the process proceeds to step S808. In step S808, live view display is started.

  In step S809, the control unit 105 calculates the length of the optimum focus detection pixel accumulation period for performing focus detection (AF). In step S810, the control unit 105 checks the flicker correction flag and determines whether to perform flicker correction. 11 and 12 are diagrams illustrating an example of the accumulation period setting method in steps S810 to S812. As described above, the control unit 105 of the present embodiment can independently control the accumulation period of the imaging pixels and the accumulation period of the focus detection pixels. FIG. 11 illustrates a case where the accumulation period of the focus detection pixels is controlled to be shorter than the accumulation period of the imaging pixels, and FIG. 12 illustrates a case where the accumulation period of the focus detection pixels is controlled to be longer than the accumulation period of the imaging pixels. Show.

  If the flicker correction flag is ON, the process proceeds to step S811, and the focus detection pixel accumulation period calculated in step S809 is corrected so as to suppress flicker as shown in FIG. 11B or 12B. To do. For example, flicker can be suppressed by setting the length of the focus detection pixel accumulation period to a flicker cycle or an integer multiple thereof as shown by black circles in FIGS. In step S812, an accumulation period after flicker correction is set.

  At this time, flicker correction is similarly performed for the accumulation period of the imaging pixels, but the accumulation period of the focus detection pixels is not necessarily corrected to the same length as the accumulation period of the imaging pixels. As the accumulation period of the focus detection pixels, an optimum one for focus detection may be selected from the lengths of a plurality of accumulation periods in which flicker is suppressed. For example, as shown in FIG. 11B or FIG. 12B, the one closest to the length of the accumulation period calculated in step S809 is selected from the lengths of the plurality of accumulation periods in which flicker is suppressed. And set.

  On the other hand, if the flicker correction flag is OFF in step S810, step S811 is skipped and the process proceeds to S812. Then, as shown in FIG. 11A or FIG. 12A, the accumulation period of the focus detection pixels calculated in step S809 is set as it is.

  In step S813, the control unit 105 determines whether a live view end operation has been performed by a photographer or the like. When the live view end operation is performed (YES), the process proceeds to step S814 to end the live view display, and the process proceeds to step S815 to end the live view. On the other hand, if the live view end operation has not been performed (NO), the process returns to step S809, and the same calculation / correction processing of the focus detection pixel accumulation period is repeated for each frame.

  As described above, the imaging apparatus according to the present embodiment is based on an imaging pixel that outputs an imaging signal based on an image formed by an imaging optical system and a plurality of images that pass through different pupil regions of the imaging optical system. An imaging device having a focus detection pixel that outputs a phase difference signal is provided. When the flicker detection unit detects flicker, the flicker correction of the phase difference signal is performed by controlling the accumulation period of the focus detection pixel independently of the accumulation period of the imaging pixel. With such a configuration, it is possible to provide an imaging apparatus capable of performing focus detection by a phase difference method with high accuracy even under a flicker light source and a control method thereof.

(Second Embodiment)
An imaging apparatus 100 and a control method thereof according to the second embodiment will be described with reference to FIGS. FIG. 13 is a flowchart illustrating a method for controlling the imaging apparatus 100 according to the second embodiment. In the flowchart of the present embodiment shown in FIG. 13, steps S804 and S805 in the flowchart shown in FIG. 9 are omitted. That is, in this embodiment, flicker correction is performed when the flicker detection unit 102 detects flicker regardless of the amplitude of the flicker. Other processes are almost the same as those in FIG. Hereinafter, processing different from FIG. 9 will be described.

  The processing up to step S802 is the same as in FIG. In step S <b> 1301, the control unit 105 determines whether or not flicker is detected by the flicker detection unit 102. If flicker is detected (YES), the process proceeds to step S806, the flicker correction flag is set to ON, and the process proceeds to step S808. On the other hand, if no flicker is detected (NO), the process proceeds to step S807, the flicker correction flag is set to OFF, and the process proceeds to step S808. In step S808, live view display is started. In the present embodiment, the flicker amplitude calculation process shown in step S804 of FIG. 9 and the flicker amplitude determination process shown in step S805 are omitted.

  In step S809, the control unit 105 calculates the optimum length of the accumulation period for performing focus detection (AF). In step S810, the control unit 105 checks the flicker correction flag and determines whether to perform flicker correction. FIG. 14 is a diagram illustrating an example of the accumulation period setting method in steps S810 to S812. FIG. 14A shows a case where the accumulation period of the focus detection pixels is controlled to be shorter than the accumulation period of the imaging pixels, and FIG. 14B shows that the accumulation period of the focus detection pixels is longer than the accumulation period of the imaging pixels. The case where it was controlled for a long time is shown.

  If the flicker correction flag is ON, the process proceeds to step S1302, and the length of the focus detection pixel accumulation period calculated in step S809 is set to the same length as the flicker-corrected imaging pixel accumulation period as shown in FIG. to correct. In step S812, an accumulation period after flicker correction is set.

  On the other hand, if the flicker correction flag is OFF in step S810, step S1302 is skipped and the process proceeds to S812. Then, as shown in FIG. 11A or FIG. 12A, the accumulation period of the focus detection pixels calculated in step S809 is set as it is.

  As described above, in the present embodiment, when the flicker detection unit detects flicker, the length of the focus detection pixel accumulation period is set to the same length as the imaging pixel accumulation period, and the flicker of the phase difference signal is set. Make corrections. As a result, the accuracy of focus detection by the phase difference method can be maintained even under a flicker light source.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be made. For example, the configuration of the imaging apparatus 100 described in the above embodiment is an example, and the imaging apparatus 100 to which the present invention is applicable is not limited to such a configuration.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 100: Image pick-up device 101: Image pick-up element 102: Flicker detection part 105: Control part 201: Pixel array 202: Vertical scanning circuit 203: Read-out circuit 204: Horizontal scanning circuit 300: Pixel unit 301, 302: Photoelectric conversion part 303: Floating diffusion Region 304: amplification transistor 305: reset transistor 306: selection transistor 307, 308: transfer transistor

Claims (12)

An imaging element having an imaging pixel that outputs an imaging signal based on an image formed by the imaging optical system, and a focus detection pixel that outputs a phase difference signal based on a plurality of images that have passed through different pupil regions of the imaging optical system When,
A flicker detection unit for detecting flicker based on the imaging signal;
A control unit that controls flicker correction of the phase difference signal by controlling the accumulation period of the focus detection pixels independently of the accumulation period of the imaging pixels when the flicker detection unit detects flicker;
An imaging apparatus comprising: The image sensor is
A pixel array in which the imaging pixels and the focus detection pixels are arranged in a matrix;
Vertical scanning for performing a first scan for reading the imaging signal from a plurality of rows in which the imaging pixels are arranged and a second scanning for reading out the phase difference signal from the plurality of rows in which the focus detection pixels are arranged. Circuit,
Have
The imaging apparatus according to claim 1, wherein the vertical scanning circuit performs the second scanning after performing the first scanning. The imaging pixel and the focus detection pixel include an A pixel that outputs an A signal and a B pixel that outputs a B signal,
The imaging element reads the imaging signal obtained by adding the A signal and the B signal in the first scanning, and the pair of the A signal and the B signal in the second scanning. The phase difference signal is read out. The imaging apparatus according to claim 2. The flicker detection unit detects the flicker amplitude,
The imaging apparatus according to claim 1, wherein the control unit performs flicker correction when the magnitude of the detected flicker amplitude is equal to or greater than a predetermined threshold. The control unit sets the length of the accumulation period of the focus detection pixels to be a length of an accumulation period in which flicker is suppressed and is different from the accumulation period of the imaging pixels, and the phase difference signal The imaging apparatus according to claim 4, wherein flicker correction is performed. The control unit controls the accumulation period of the focus detection pixels independently of the accumulation period of the imaging pixels when the magnitude of the detected flicker amplitude is less than the threshold value, and the luminance of the phase difference signal The imaging apparatus according to claim 4, wherein the imaging device is adjusted. When the flicker detecting unit detects flicker, the control unit sets the length of the accumulation period of the focus detection pixel to the same length as the accumulation period of the imaging pixel, and performs flicker correction of the phase difference signal. The imaging apparatus according to any one of claims 1 to 3, wherein: The flicker detection unit detects a flicker cycle,
The control unit performs flicker correction on the phase difference signal by setting the length of the accumulation period of the focus detection pixels to the flicker cycle or an integer multiple of the flicker cycle. 8. The imaging device according to any one of items 7. The imaging apparatus according to claim 1, wherein the flicker detection unit detects the flicker by comparing the imaging signals between consecutive frames. An imaging element having an imaging pixel that outputs an imaging signal based on an image formed by the imaging optical system, and a focus detection pixel that outputs a phase difference signal based on a plurality of images that have passed through different pupil regions of the imaging optical system A method for controlling an imaging apparatus comprising:
A flicker detection step for detecting flicker based on the imaging signal;
A control step of performing flicker correction of the phase difference signal by controlling the accumulation period of the focus detection pixels independently of the accumulation period of the imaging pixels when flicker is detected in the flicker detection step;
A method for controlling an imaging apparatus, comprising: An imaging element having an imaging pixel that outputs an imaging signal based on an image formed by the imaging optical system, and a focus detection pixel that outputs a phase difference signal based on a plurality of images that have passed through different pupil regions of the imaging optical system In an imaging apparatus comprising:
Flicker detection means for detecting flicker based on the imaging signal;
Control means for controlling flicker correction of the phase difference signal by controlling the accumulation period of the focus detection pixels independently of the accumulation period of the imaging pixels when the flicker detection means detects flicker;
A program characterized by functioning as   A computer-readable storage medium storing the program according to claim 11.