JP6294607B2 - IMAGING DEVICE, ITS CONTROL METHOD, PROGRAM, AND STORAGE MEDIUM - Google Patents

Description

  The present invention relates to a technique for suppressing flicker in an imaging apparatus.

  An imaging apparatus such as a digital camera has an electronic viewfinder function (EVF) that displays a through image (or live view image) on a display during a shooting preparation operation. The imaging apparatus includes a first switch that is turned on when the shutter button is half-pressed and outputs a first switch signal SW1, and a second switch that is turned on when the shutter button is fully pressed and outputs a second switch signal SW2. When the signal SW1 is turned on, the photographing preparation operation is started, and when the second switch signal SW2 is turned on, the main photographing is started.

  During the shooting preparation operation, automatic exposure control (AE) for determining the exposure during actual shooting and automatic focus detection (AF) for determining the focus lens position are performed. For example, the photographer performs AE processing and AF processing by turning on the first switch signal SW1 by the first switch when the angle of view to be photographed is determined, and the timing at which the photographer wants to photograph while the SW1 is in the on state (half-pressed state). Thus, the main photographing can be performed by turning on the second switch signal SW2 by the second switch.

  In general AE processing, an appropriate shooting condition (aperture value Av and shutter speed Tv (sensor sensitivity Sv as required) is used according to subject brightness, using a program diagram (P diagram) prepared in advance. ) Combination). Further, it is known that a P diagram corresponding to the application is prepared in advance and selectively used during AF or actual photographing.

  On the other hand, in the aperture control, when different P diagrams are used before the first switch signal SW1 is turned on and when the first switch signal SW1 is turned on, the second switch signal SW2 is turned on and the second switch signal SW2 is turned on. The aperture value may change. Then, even if the photographer turns on the second switch signal SW2 at a desired photographing timing while the first switch signal SW1 is on, the time required for aperture control becomes a time lag, and the main photographing is greatly deviated from the desired photographing timing. It is also possible that will be done. For such inconvenience, by setting the same aperture value when the first switch signal SW1 is ON and when the second switch signal SW2 is ON, the operation time required for aperture control at the time of actual photographing is shortened. It is possible to reduce the time lag during shooting.

  For example, Patent Document 1 describes that the aperture value used for capturing an image displayed live immediately before the recording instruction is issued from the time of recording preparation or when the recording instruction is canceled until the recording instruction is canceled. ing.

JP 2006-060409 A

  However, if the aperture value is always the same while the first switch signal SW1 is on and the second switch signal SW2 is on, inconvenience may occur in exposure control under a flicker light source, for example. A CMOS image sensor mounted as an image sensor in a digital camera or the like has different exposure timing for each line. For this reason, a horizontal stripe-like light-dark change occurs in an image signal for one frame captured under a light source (flicker light source) whose luminance periodically changes at a power supply frequency (50 Hz, 60 Hz, etc.) such as a fluorescent lamp. This light / dark change moves in the direction perpendicular to the exposure line of the image sensor with time. Such vertical periodic brightness is called flicker. As a method for suppressing such flicker, a method is known in which imaging is performed at a shutter speed of 1 / (positive integer multiple of the flicker frequency of the light source (that is, the power supply frequency)). In this case, if the flicker frequency is 50 Hz, the shutter speed is 1/50 seconds or 1/100 seconds, and if it is 60 Hz, 1/60 seconds or 1/120 seconds.

  On the other hand, there are many cameras that can set the shutter speed to a value shorter than 1/100 seconds or 1/120 seconds. If priority is given to suppression of flicker while the first switch signal SW1 is on, the shutter speed is 1/100 seconds or 1/120 seconds, and a small aperture is used. However, if the aperture is too small, there is an adverse effect on the image quality, such as a reduction in resolution due to diffraction phenomenon, so that the aperture during shooting generally has a shutter speed shorter than 1/100 sec or 1/120 sec. But I often use an open side. In other words, if priority is given to flicker suppression, the aperture value when the first switch signal SW1 is on and when the second switch signal SW2 is on cannot be set to the same value, and the time lag may not be eliminated.

  The present invention has been made in view of the above problems, and the object thereof can be appropriately switched between performing control giving priority to flicker suppression or control giving priority to time lag reduction during shooting according to the scene. It is to realize technology.

In order to solve the above problems and achieve the object, an imaging apparatus according to the present invention includes an imaging unit, a determination unit that determines a shooting condition based on subject luminance in accordance with an instruction for a shadow preparation operation, and the imaging unit. A detection unit that detects flicker based on a captured image, and a first control that prioritizes flicker suppression in exposure control from a shooting preparation state to main shooting according to the flicker detection result by the detection unit. Control means for switching to second control that prioritizes control or time lag reduction at the time of shooting. The control means detects flicker until receiving an instruction for the shooting preparation operation, and wherein after receiving instructions if flicker is detected by receiving an indication of the shooting, set the first control until receiving an instruction of the present photographing, the instruction of the photographing preparation operation If flicker is not detected until the first shooting is completed and flicker is detected after receiving the instruction for the shooting preparation operation and receiving the instruction for the main shooting, the second control is performed until the instruction for the main shooting is received. Is set.

  According to the present invention, it is possible to appropriately switch between performing control that prioritizes flicker suppression and performing control that prioritizes time lag reduction during shooting according to the scene.

The block diagram which shows the apparatus structure of embodiment which concerns on this invention. 5 is a flowchart showing imaging processing according to the present embodiment. The program diagram used for the imaging | photography process of this embodiment. 6 is a flowchart illustrating flicker detection processing according to the present embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. The embodiment described below is an example for realizing the present invention, and should be appropriately modified or changed according to the configuration and various conditions of the apparatus to which the present invention is applied. It is not limited to the embodiment. Moreover, you may comprise combining suitably one part of each embodiment mentioned later.

  Hereinafter, an embodiment in which the present invention is applied to an imaging apparatus such as a digital camera that captures a moving image or a still image will be described. Note that the present invention can be widely applied to portable electronic devices such as a smartphone equipped with a camera.

  <Apparatus Configuration> With reference to FIG. 1, an outline of the configuration and functions of an imaging apparatus according to an embodiment of the present invention will be described.

  In FIG. 1, the photographing lens 101 includes a zoom mechanism. The aperture / shutter 102 controls the charge accumulation time by adjusting the amount of light incident on the image sensor 106 of the optical image, which is the reflected light of the subject, according to the operation command of the AE (automatic exposure) processing unit 103. The AE processing unit 103 controls the operation of the aperture / shutter 102 and controls the A / D conversion unit 107. The focus lens 104 focuses on the light receiving surface of the image sensor 106 to form an optical image in accordance with a control signal from an AF (autofocus) processing unit 105. Note that the photographing lens 101, the aperture / shutter 102, and the focus lens 104 need not be arranged in the order shown in FIG.

  The image sensor 106 converts an optical image formed on the light receiving surface into an electrical signal by a photoelectric conversion element such as a CCD or a CMOS, and outputs the electrical signal to the A / D converter 107. The A / D conversion unit 107 converts the analog signal input from the image sensor 106 into a digital signal. The A / D converter 107 includes a CDS circuit that removes noise from the analog signal, and a nonlinear amplifier circuit that nonlinearly amplifies the analog signal before converting it to a digital signal.

  The image processing unit 108 performs predetermined resizing processing such as pixel interpolation and image reduction and color conversion processing on the digital signal output from the A / D conversion unit 107, and outputs image data. The format conversion unit 109 performs format conversion of the image data generated by the image processing unit 108 in order to store the image data in the DRAM 110. The DRAM 110 is an example of a high-speed built-in memory, and is used as a high-speed buffer that manages temporary storage of image data, or as a working memory in image data compression / decompression processing.

  The image recording unit 111 includes a recording medium such as a memory card that records captured images (still images and moving images) and an interface thereof. The system control unit 112 includes a CPU, a ROM, and a RAM. The CPU expands and executes a program stored in the ROM in a work area of the RAM, thereby controlling the operation of the entire apparatus. In addition, the system control unit 112 performs control by selecting a mode to be implemented from among a plurality of charge accumulation control modes of the image sensor 106. The VRAM 113 is an image display memory. The display unit 114 is, for example, an LCD or the like, and displays an imaging screen and a distance measurement area at the time of shooting, in addition to displaying an image, a display for assisting operations, and a camera status display.

  The photographer operates the operation unit 115 to operate the apparatus from the outside. The operation unit 115 includes, for example, a menu switch for performing various settings such as exposure correction, aperture value setting, and image reproduction setting, a zoom lever for instructing a zoom operation of the photographing lens, and an operation mode switching switch between the photographing mode and the reproduction mode Etc. The main switch 116 is a switch for turning on the system. The first switch 117 is a switch for outputting the first switch signal SW1 to the system control unit 112 and performing a shooting preparation operation such as AE processing or AF processing. The second switch 118 is a switch for outputting the second switch signal SW2 to the system control unit 112 and instructing photographing while the first switch signal SW1 by the first switch 117 is on (in the photographing preparation state).

  <Shooting Process> Next, referring to FIG. 2, it is a shooting process by the imaging apparatus of the present embodiment, in which exposure control giving priority to flicker suppression or exposure control giving priority to time lag reduction at the time of shooting according to the scene. The switching process will be described. The processing in FIG. 2 is realized by the CPU of the system control unit 112 developing and executing a program stored in the ROM in the RAM work area. Note that the flicker detected in this embodiment is under a 50 Hz light source.

  In step S201, the system control unit 112 performs flicker detection until the first switch signal SW1 by the first switch 117 is turned on. The flicker detection method will be described in detail with reference to FIG.

  In step S202, the system control unit 112 determines whether flicker is detected in step S201. If flicker is detected, the process proceeds to step S203, and if not, the process proceeds to step S204.

  In step S203, since the flicker is detected, the system control unit 112 switches to the first exposure control so that Tv gives priority to flicker suppression. The details of the exposure control will be described in detail with reference to FIG.

  In step S204, since flicker is not detected, the system control unit 112 uses the same aperture as the AF processing in the shooting preparation state (while the first switch signal SW1 is on) as exposure control that prioritizes time lag reduction during shooting. Switch to the second exposure control set to the value.

  In step S205, the system control unit 112 waits for an instruction to shift to the shooting preparation operation (the first switch signal SW1 is turned on), and proceeds to step S206 if the shift instruction is received. Note that flicker detection is always performed until the first switch signal SW1 is turned on or flicker is suppressed. Alternatively, flicker detection may be performed only when the main switch 116 is turned on, and exposure control to be performed may be determined according to the detection result.

  In step S206, the system control unit 112 performs AE processing and AF processing in the shooting preparation state (while the first switch signal SW1 is on). Specifically, first, the AE processing unit 103 executes AE processing for setting an exposure condition when executing AF processing. In the AE process, an appropriate shooting condition (a combination of an aperture value Av and a shutter speed Tv (a sensitivity Sv equivalent to ISO if necessary)) corresponding to the subject brightness is determined using a program diagram to be described later. After the AE process, the AF processing unit 105 performs the AF process. As the AF processing, for example, a method is adopted in which the lens position where the high frequency component of the luminance signal of the subject obtained from the image sensor 106 is maximized is set to the in-focus position. Specifically, the focus lens 104 is driven over the entire distance measurement range, and an evaluation value based on the high frequency component of the luminance signal obtained from the image sensor 106 is stored each time, and the maximum value of the stored values AF processing is performed by a scanning method in which the lens position corresponding to is the in-focus position.

In steps S207 to S209, the system control unit 112 performs flicker detection, and sets the exposure condition for the main photographing according to the detection result. Specifically, if flicker is detected in step S207, the process proceeds to step S208, and if not, the process proceeds to step S209. In the case where at least one of the optical viewfinder and the electronic viewfinder function (EVF) is provided and the optical viewfinder is used without using the EVF, it is not necessary to consider flicker. Even if is detected, the process proceeds to step S209. Also, when the first switch signal SW1 and the second switch signal SW2 are continuously turned on within a predetermined time, the time affected by flicker is short while the first switch signal SW1 is on, and the photographing is performed. Since it can be determined that the person wants to shoot immediately, the process proceeds to step S209.
Furthermore, in the case of having a continuous shooting function for continuously shooting still images, in the continuous shooting mode, since the flicker suppression is prioritized during the first shooting, the process proceeds to step S208, and the second and subsequent shootings are continuously performed. Proceed to step S209 to prioritize the copying speed. On the other hand, when the servo control that can continue the AE / AF processing is possible while the first switch signal SW1 is ON, the diaphragm can be freely operated during the servo control.

  In step S208, since the flicker is detected in the shooting preparation state (while the first switch signal SW1 is on), the system control unit 112 performs first exposure control so that Tv is given priority to flicker suppression.

  In step S209, since the flicker is not detected in the shooting preparation state (while the first switch signal SW1 is on), the system control unit 112 switches to the second exposure control that prioritizes the reduction of the time lag during shooting. In the second exposure control, the same aperture value as that at the time of actual photographing (the second switch signal SW2 is turned on) is set. Note that flicker is not detected before the transition to the shooting preparation operation (before the first switch signal SW1 is turned on) (step S201), and flicker is detected after the shooting preparation operation (after the first switch signal SW1 is turned on). In this case, the exposure control may be switched to give priority to the reduction of the time lag during shooting. In this case, there is a possibility that the subject or the camera has moved and the scene has changed after the first switch signal SW1 is turned on, and there is an advantage that priority is given to reducing the time lag.

  When the second switch signal SW2 is turned on in step S210 and an instruction to shift to the main shooting is received, the system control unit 112 proceeds to step S211 to perform exposure control for the main shooting, and performs the main shooting in step S212. carry out.

  As described above, according to this embodiment, it is possible to appropriately switch between performing control that prioritizes flicker suppression and performing control that prioritizes time lag reduction during shooting. In this embodiment, an example in which 50 Hz flicker is detected has been described. However, when 50 Hz and 60 Hz flicker can be detected, Tv is given priority to 50 Hz flicker suppression according to the flicker detection result in step S202. The exposure control is such that the exposure control is such that the Tv gives priority to 60 Hz flicker suppression, and the exposure control gives the same aperture value as the AF processing in the shooting preparation state giving priority to reducing the time lag. You may control to. Similarly, according to the flicker detection result in step S207, exposure control that gives priority to Tv giving priority to 50Hz flicker suppression, exposure control to give Tv giving priority to suppression of 60Hz flicker, and shooting that gives priority to time lag reduction It may be controlled to branch to any one of the exposure controls so that the same aperture value is obtained.

  <Program Diagram> Next, with reference to FIG. 3, a program diagram (hereinafter referred to as a P diagram) used in the photographing process of this embodiment will be described. Note that these P diagrams are stored in the ROM or RAM of the system control unit 112. In this embodiment, the aperture value is Av2 to 6 (F2.0 to F8.0), the shutter speed is Tv0 to 11 (1 second to 1/2000 second), and the gain increase amount is Gain0 to 4 (ISO100 to ISO1600). ) Can be set. The gain increase amount is controlled by the AE processing unit 103 that has received a control command from the system control unit 112.

  FIG. 3 shows the state before the first switch signal SW1 is turned on (when a through image is captured), while SW1 is turned on (flicker detection) (a), during AF processing while SW1 is on (b), and when SW1 is on (flicker not detected) (c) ), And each P diagram at the time of actual photographing (d).

  In FIG. 3, the solid line indicates the aperture value Av, the broken line indicates the shutter speed Tv, and the dotted line indicates the Gain value. The horizontal axis represents the subject brightness, and the brightness increases as going to the right side of the horizontal axis. The vertical axis represents the aperture value Av, the shutter speed Tv, and the gain value, and the values increase as going upward on the vertical axis. The system control unit 112 calculates the subject brightness from the image signal obtained from the image sensor 106, the aperture value Av and shutter speed Tv of the aperture / shutter 102, and the Gain value.

  Generally, as the subject brightness decreases, Av and Tv are decreased and the Gain value is increased. In other words, the aperture is set wide, the shutter speed is set low, and the gain increase amount is increased so that an appropriate image can be taken for a dark scene. On the other hand, Av and Tv are increased and the Gain value is decreased as the subject brightness increases. That is, the aperture is made small, the shutter speed is increased, and the gain increase amount is decreased.

  In the present embodiment, the shutter speed is limited to 1/30 second or less before the first switch signal SW1 is turned on (when a through image is captured), while SW1 is turned on (a) and during AF processing (b). Before SW1 is turned on and while SW1 is turned on, if the shutter speed becomes slow, it becomes difficult for the photographer to adjust the angle of view. In order to avoid such inconvenience, only an appropriate shutter speed can be used. I am doing so. Further, at the time of AF processing (b), if the shutter speed is slow, it is difficult to acquire a frequency component due to camera shake or subject blur. In this embodiment, the upper limit and the lower limit of the aperture value and the Gain value are the same for any scene, but the upper limit and the lower limit are set so that appropriate processing can be performed for each scene, as with the shutter speed. The lower limit may be a different value.

  In FIG. 3A, a region [A1] represents a behavior at low luminance. In the area [A1], Tv is changed according to the luminance. In the area [B1] brighter than the luminance at which Tv is a predetermined value, the Gain value is changed. The predetermined value is a shutter speed of 1 / (positive integer multiple of the flicker frequency of the light source). When 50 Hz flicker is detected, the shutter speed is set to 1/50 second or 1/100 second. On the other hand, when 60 Hz flicker is detected, the shutter speed is set to 1/60 seconds or 1/120 seconds. Further, there may be a case where only one of 50 Hz and 60 Hz flicker can be detected. In this case, the shutter speed is set to 1/50 (or 60) seconds or 1/100 (or 120) seconds when 50 (or 60) Hz flicker is detected, and 1/60 when flicker is not detected. (Or 50) seconds or 1/120 (or 100) seconds may be set. In the region [C1] brighter than the luminance at which the Gain value is the minimum value, Av is changed while Tv is fixed. This is because Tv capable of suppressing flicker is given priority as much as possible. In the region [D1] brighter than the luminance that is a small aperture for which Av can be set, Tv is changed.

  In FIG. 3B, a region [A2] represents a behavior at low luminance. In the area [A2], the Gain value is changed according to the luminance. In the region [B2] brighter than the luminance at which the Gain value is the minimum value, Tv is changed. In the area [C2] brighter than the luminance at which Tv is the maximum value, Av is changed to a small aperture. The reason is as follows. That is, it is known that, in AF processing that determines the in-focus position using contrast data obtained from an image signal, generally a scene with a small Av and Gain value has higher performance. This is because the depth of field becomes shallower as the Av is reduced (the aperture is moved closer to the open position), and the difference between the focused portion and the unfocused portion becomes easier to understand. That is, since the peak value of the contrast data becomes easier to understand as the aperture is moved closer to the full aperture, accurate focusing becomes easier. On the other hand, increasing the Gain value amplifies the image signal output from the image sensor 106, but in this case, noise is also amplified. Then, the influence of the noise on the contrast data becomes large, and the peak value of the contrast data may be erroneously determined, leading to a decrease in AF performance. For this reason, focus is placed on AF accuracy, and a P diagram with priority to the wide aperture and low sensitivity is used.

  In FIG. 3C, a region [A3] represents a behavior at low luminance. In the area [A3], Tv is changed according to the luminance. In the region [B3] brighter than the luminance at which Tv is a predetermined value, the Gain value is changed. The predetermined value is a shutter speed 1 / (a positive integer multiple of the flicker frequency of the light source) as in FIG. In the region [C3] brighter than the luminance at which the Gain value is the minimum value, Av is changed. In the area [D3] where Av is brighter than a predetermined value, Tv is changed. In the region [E3] where Tv is brighter than a predetermined value, Av is changed. Av, which is the boundary between [B3] and [C3], the boundary between [C3] and [D3], and the boundary between [D3] and [E3], is set to the same value at all brightnesses, as will be described later. It is set. This is to prevent the time required for aperture control from being added as a time lag by setting Av to the same value when the second switch signal SW2 is turned on while the first switch signal SW1 is turned on to set Av to the same value. is there. Further, when the same aperture value as that used in the actual photographing is used during the AF process, depending on the aperture value, the subject depth may be deepened and the AF accuracy may be reduced. In order to cope with this, a P diagram is set so that the aperture value is the same within the predetermined range from the widest aperture that can guarantee high accuracy, and the aperture value is the same at the time of actual photographing and AF processing. You may do it. In the case of a digital camera that can be switched to a plurality of shooting modes, the P diagram may be changed for each shooting mode.

  In FIG. 3D, a region [A4] represents a behavior at low luminance. In the area [A4], Tv is changed according to the luminance, and as the shutter speed becomes slower (exposure time becomes longer), camera shake and subject blur tend to occur. Tv is lowered as the value increases. In the region [B4] where Tv is equal to or greater than the threshold value, the Gain value is changed. As the amount of gain increases, noise increases in the captured image and the appearance deteriorates. Therefore, in the case of Tv that can suppress camera shake and subject blur, the shutter speed becomes higher as the brightness increases. Reduce the gain increase amount. As a result, it is possible to take a good-looking image.

  In the region [C4] brighter than the luminance at which the Gain value is minimized, Av is changed. Depending on the type of lens, it is possible to shoot a high-resolution image when the aperture is stopped to some extent rather than an open aperture. Therefore, if the brightness is such that camera shake, subject blur, and noise can be suppressed, the aperture value is set so that a high-resolution image can be taken. In a region [D4] brighter than the aperture value at which a high-resolution image can be taken, Tv is changed. As described above, if the aperture is too small, there is an adverse effect on the image quality, such as a decrease in resolution due to the diffraction phenomenon. . Then, Av is changed in a region [E4] brighter than the upper limit that Tv can be set. In the case of a digital camera that can be switched to a plurality of shooting modes, the P diagram may be changed for each shooting mode.

  As described above, according to the present embodiment, when flicker is detected, the P diagram when the first switch signal SW1 is ON is set to flicker suppression priority, and when flicker is not detected, the P diagram is switched to time lag reduction priority. It becomes possible.

  If the scene cannot be set to 1 / (a positive integer multiple of the flicker frequency of the light source), that is, a reciprocal of a positive integer multiple of the flicker frequency of the light source, because of high brightness or low brightness, flicker. It becomes difficult to suppress. In this case, flicker correction means by image processing is provided, and flicker correction is performed only for scenes that cannot be set to a shutter speed of 1 / (positive integer multiple of the light source flicker frequency). By doing so, flicker can be suppressed in any scene.

  For example, as a flicker correction method, there is a method in which a frequency component of a flicker light source is detected from a moving image signal and a correction value is multiplied only in an area where flicker occurs. Specifically, first, each frame of the moving image is vertically divided into N lines, and the luminance integrated value of each line is calculated. Then, only the flicker component is calculated by subtracting, for each line, the luminance integral value of each line calculated in the same manner for the image one frame before in time series. From the flicker component information of each line, the amplitude and flicker frequency of the luminance change by the flicker light source are calculated by Fourier transform, and the correction value at each frame is calculated. Then, the correction value is multiplied to the line having the influence of flicker in each frame. Such a method makes it possible to correct flicker.

  <Flicker Detection> Next, the flicker detection process in S201 of FIG. 2 will be described with reference to FIG. Hereinafter, a flicker detection method under a 50 Hz light source will be described.

  In step S401, the system control unit 112 sets the gain increase Tv of the P diagram for capturing a through image before the first switch signal SW1 is turned on to 1/60 seconds and 1/120 seconds. Thus, although it is possible to suppress flicker of a through image captured under a 60 Hz flicker light source, it is difficult to suppress flicker of a through image captured under a 50 Hz flicker light source.

  In step S402, the system control unit 112 calculates a luminance histogram Yf [i] for the current frame image of the through image by the image processing unit 108. i is the number of divisions of the luminance histogram. For example, the luminance value that each pixel of the image can take is 0 to 255, and the value i can take is 0 to 31. At this time, Yf [0] is the sum of the number of pixels having luminance values of 0 to 7, Yf [1] is the sum of the number of pixels having luminance values of 8 to 15, and Yf [31] is the luminance value of 248 to 255. Is the sum of the number of pixels.

  In step S403, the system control unit 112 determines whether or not the image processing unit 108 has calculated the luminance histogram more than a predetermined number of times (CalcNum + 1) necessary for flicker detection. If the number is not sufficient, the system control unit 112 ends the process and waits until the next frame image is captured. If the brightness histogram has been calculated a predetermined number of times or more, the system control unit 112 proceeds to step S404.

In step S <b> 404, the system control unit 112 sequentially calculates the difference sum of the luminance histograms between two consecutive frame images for the luminance histograms calculated from a plurality of (CalcNum + 1) frame images that are continuous through images. This difference sum is a value obtained by dividing the luminance histogram between two consecutive frame images into a plurality of regions and summing up the differences for each region. For example, when n = 0, the system control unit 112 calculates and compares the difference sum between the luminance histograms of the current frame image and the previous frame image. If the luminance histogram of the current frame image is Yf [i] [0] and the luminance histogram of the previous frame image is Yf [i] [1], the difference is DiffSum [0] = Σ (Yf [i] [ 0] −Yf [i] [1]) (i = 0, 1,..., 31)
It becomes.

  In step S405, the system control unit 112 calculates the maximum value and minimum value of DiffSum [n] acquired in step S404, and the difference Delta thereof.

  In step S406, the system control unit 112 determines that there is a possibility that the through image includes a flicker component (flicker occurs) if the value of Delta is equal to or higher than the lower limit value Th_Min and lower than the upper limit value Th_Over. . The system control unit 112 determines that the flicker component is not included in the through image when the value of Delta is less than the lower limit value Th_Min, and there is a possibility of false detection when the value exceeds the upper limit value Th_Over. Is determined.

  Next, when it is determined in step S406 that there is a possibility of occurrence of flicker, the system control unit 112 increments the flicker detection count Count by 1 (S407), and otherwise initializes the count ( Count = 0) (S408). This is in order to suppress false detection of flicker. If it is determined that flicker occurs only when the value of Delta once falls within the range between the upper limit value and the lower limit value (Th_Min ≦ Delta ≦ Th_Over). This is because there is a possibility that the flicker is erroneously detected.

  In steps S409 and S410, when it is determined that there is a possibility that a flicker component may be included in the latest (CalcNum + 1) frame image continuously for a certain period, it is determined that the image is captured under a 50 Hz flicker light source. Specifically, when the flicker detection count Count is equal to or greater than a predetermined threshold Th_Count in step S409, the system control unit 112 determines that 50 Hz flicker has been detected. Then, in order to suppress 50 Hz flicker, the gain increase Tv in the P diagram for capturing a through image is changed to 1/50 seconds and 1/100 seconds (S410).

  In the present embodiment, flicker detection under a 50 Hz light source has been described. However, if the gain increase Tv is set to 1/50 second in step S401 and the processing in steps S402 to S409 is performed, flicker under a 60 Hz light source is detected. It becomes possible to detect. For example, in step S401, the gain increase Tv is set to 1/60 second and the process up to step S409 is performed. After a predetermined time has elapsed, the gain increase Tv is set to 1/50 second in step S401 and the same process is performed. Do. In this way, it is possible to determine whether 50 Hz flicker is detected, 60 Hz flicker is detected, or no flicker is detected.

  [Other Embodiments] The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads and executes the program code. It is processing to do. In this case, the program and the storage medium storing the program constitute the present invention.

Claims (14)

Imaging means;
A determining means for determining shooting conditions based on subject brightness in accordance with an instruction for shooting preparation operation;
Detecting means for detecting flicker based on an image picked up by the image pickup means;
According to the flicker detection result by the detection means, the first control giving priority to the flicker suppression or the second control giving priority to the reduction of the time lag at the time of shooting from the shooting preparation state to the main shooting. Control means for switching to,
Wherein, the flicker until receiving an indication of the photographic preparation operation is detected, wherein when the flicker until receiving an indication of the present shooting instruction receiving from the photographing preparation operation is detected, the present until receiving an instruction to photographing setting the first control, the not detected flicker until receiving an instruction for photographing preparation operation, from receiving the indication of the photographic preparation operation until it receives an instruction of the present photographing An image pickup apparatus, wherein when the flicker is detected, the second control is set until an instruction for the main photographing is received.   2. The imaging apparatus according to claim 1, wherein in the second control, a diaphragm value that adjusts an amount of incident light on the imaging unit from the imaging preparation state to the main imaging is set to the same value.   3. The imaging apparatus according to claim 1, wherein, in the first control, an exposure time of the imaging unit is set to a reciprocal of a positive integer multiple of a flicker frequency detected by the detection unit. .   If the flicker is not detected before receiving the instruction for the shooting preparation operation, or if the flicker is not detected before receiving the instruction for the main shooting after receiving the instruction for the shooting preparation operation, The imaging device according to claim 1, wherein the imaging device is switched to the second control. It has at least one of optical viewfinder and electronic viewfinder functions,
The imaging apparatus according to claim 1, wherein when the electronic viewfinder function is not operated, switching to the second control is performed.   The control means switches to the second control when the instruction for the photographing preparation operation and the instruction for the main photographing are continuously performed within a predetermined time. The imaging device according to any one of the above.   4. The control unit according to claim 1, wherein the control unit switches to the second control after the first image is taken in accordance with the instruction of the main shooting in the continuous shooting mode. 5. The imaging device described. A correction means for correcting the flicker by image processing;
In the first control, when the exposure time of the imaging unit cannot be set to a reciprocal of a positive integer multiple of the flicker frequency detected by the detection unit, the correction unit corrects the flicker. The imaging apparatus according to claim 3. An image sensor;
Instruction means capable of instructing a shooting preparation operation and a shooting operation when imaging a subject using the imaging device;
Setting means for setting exposure control data for setting an exposure condition including an aperture value, a charge accumulation time, and a gain amount according to a change in luminance of the subject,
The setting means differs in the brightness of the subject when changing the aperture value depending on whether flicker occurs during the shooting preparation operation instruction or when flicker does not occur. An image pickup apparatus, wherein the exposure control data is set so that the brightness of the subject when the aperture value is changed is the same when no image is generated and when the photographing operation is instructed.   The imaging apparatus according to claim 9, wherein the exposure control data is data that is different during an instruction for a photographing preparation operation and after an instruction for a photographing operation. A determination step of determining shooting conditions based on subject brightness in accordance with an instruction for shooting preparation operation;
A detection step of detecting flicker based on an image captured by the imaging means;
Control for switching the exposure control from the shooting preparation state to the actual shooting according to the flicker detection result to the first control giving priority to the flicker suppression or the second control giving priority to the time lag reduction at the time of shooting. And having a process
Wherein in the control step, the flicker until receiving an indication of the photographic preparation operation is detected, wherein when the flicker until receiving an indication of the present shooting instruction from receiving by the photographic preparation operation is detected, the present until receiving an instruction to photographing setting the first control, the not detected flicker until receiving an instruction for photographing preparation operation, from receiving the indication of the photographic preparation operation until it receives an instruction of the present photographing A method of controlling an image pickup apparatus, wherein when the flicker is detected, the second control is set until an instruction for the main photographing is received. An imaging device control method comprising: an imaging element; and an instruction unit capable of instructing an imaging preparation operation and an imaging operation,
A setting step for setting exposure control data for setting an exposure condition including an aperture value, a charge accumulation time, and a gain amount according to a change in luminance of the subject;
In the setting step, the brightness of the subject when changing the aperture value differs between when flicker occurs during the shooting preparation operation instruction and when flicker does not occur, and flicker occurs during the shooting preparation operation instruction. A control method for an imaging apparatus, wherein the exposure control data is set so that the brightness of the subject when the aperture value is changed is the same when no shooting occurs and when an imaging operation is instructed.   The program for functioning a computer as each means of the imaging device of any one of Claim 1 thru | or 10.   A computer-readable storage medium storing a program for causing a computer to function as each unit of the imaging apparatus according to any one of claims 1 to 10.

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