JP6556480B2 - Imaging apparatus and imaging method - Google Patents

Description

  The present invention relates to an imaging apparatus and an imaging method capable of performing exposure control so that an appropriate exposure amount is obtained even when an aperture value is changed during moving image shooting or live view display.

  In an imaging apparatus such as a camera, the appropriate exposure amount is maintained by simultaneously adjusting the electronic shutter speed and ISO sensitivity when driving the aperture during moving image shooting or live view display. However, since the diaphragm is mechanically driven, there is a delay in movement, whereas the electronic shutter speed and ISO sensitivity are electrically controlled, so there is almost no time delay in the changing operation. . For this reason, a time difference occurs until the desired exposure is reached, and flickering occurs in the moving image or the live display image, resulting in an unsightly screen.

  Therefore, the predicted value of the current aperture position is calculated from the aperture driving speed and the target value, and the electronic shutter speed and the ISO sensitivity exposure setting are operated according to the predicted aperture value based on the predicted value. An imaging device has been proposed (see Patent Document 1).

JP2013-031010A

  In the above-described Patent Document 1, since the electronic shutter speed and ISO sensitivity are controlled based on the predicted aperture value, it is possible to suppress exposure fluctuations and reduce screen flicker. However, it is difficult to make the predicted value and the actual aperture value completely coincide with each other. For this reason, the exposure fluctuates during moving image shooting or live view display, and the image flickers.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an imaging apparatus and an imaging method in which an image does not flicker even if an aperture value is changed.

In order to achieve the above object, an image pickup apparatus according to a first aspect of the present invention includes an image pickup device that picks up subject light that has passed through a photographing optical system and generates a pixel signal, and an aperture that restricts a light beam that has passed through the photographing optical system. Amplifying means for amplifying the pixel signal generated by the image sensor at a predetermined gain; and changing the aperture of the diaphragm and the gain of the amplifying means to change image data based on the pixel signal generated by the image sensor Control means for adjusting the exposure amount, and the control means drives the diaphragm and adjusts the exposure amount by changing the aperture so that the change amount of the exposure amount per unit time is constant. The exposure amount is adjusted by continuously changing the amplification factor of the amplifying means based on the change in the aperture of the diaphragm so that the change amount of the exposure amount per unit time is constant.

The imaging apparatus according to a second invention is the imaging device according to the first invention, wherein when the control means drives the diaphragm to change the aperture and the aperture limit is reached, the gain of the amplifying device is increased. Change the exposure amount.

An image pickup apparatus according to a third aspect of the invention is an image pickup device that picks up subject light that has passed through a photographing optical system to generate a pixel signal, a diaphragm that restricts a light beam that has passed through the photographing optical system, and an electronic device of the image pickup device. An electronic shutter speed setting means for setting a shutter speed, and an aperture amount of the diaphragm and an electronic shutter speed of the electronic shutter speed setting means are changed to adjust an exposure amount of image data based on a pixel signal generated by the image sensor. Control means, and the control means drives the diaphragm to adjust the exposure amount by changing the aperture so that the change amount of the exposure amount per unit time is constant, and then continuously based on the exposure amount of change due to the change of the aperture of the diaphragm regulate the exposure amount was varied as the amount of change in the exposure amount per electronic shutter speed unit time of the electronic shutter speed setting means is constant To.
According to a fourth aspect of the present invention, in the image pickup apparatus according to the third aspect, the control unit is configured so that the change amount of the exposure amount matches the change amount of the exposure amount according to the change of the aperture of the diaphragm. The electronic shutter speed of the electronic shutter speed setting means is changed.
The image pickup apparatus according to a fifth invention is the imaging device according to the third or fourth invention, wherein the control means drives the diaphragm and changes the aperture, and the electronic shutter speed is reached when the aperture limit is reached. The exposure amount is adjusted by changing the electronic shutter speed of the setting means.

An imaging method according to a sixth aspect of the present invention is an imaging apparatus comprising: an imaging element that captures subject light that has passed through a photographing optical system to generate a pixel signal; and a diaphragm that restricts a light beam that has passed through the photographing optical system. In the imaging method of the above, the pixel signal generated by the imaging device is amplified at a predetermined amplification factor, and the aperture of the diaphragm and the amplification factor are changed, so that the exposure amount of image data based on the pixel signal generated by the imaging device After adjusting the exposure amount by changing the aperture so that the amount of change in the exposure amount per unit time is constant, the aperture is continuously adjusted based on the change in the aperture of the aperture. Thus, the exposure amount is adjusted by changing the amplification factor so that the change amount of the exposure amount per unit time is constant.

An image pickup method according to a seventh aspect of the present invention is an image pickup apparatus comprising: an image pickup element that picks up subject light that has passed through a photographing optical system and generates a pixel signal; and a diaphragm that restricts a light beam that has passed through the photographing optical system. In the imaging method in the above, the electronic shutter speed of the image sensor is set, the aperture of the diaphragm and the electronic shutter speed are changed, and the exposure amount of the image data based on the pixel signal generated by the image sensor is adjusted. After adjusting the exposure amount by driving the aperture and changing the aperture so that the amount of change in the exposure amount per unit time is constant, it is continuously based on the change in the exposure amount due to the aperture variation of the aperture. Thus, the exposure amount is adjusted by changing the electronic shutter speed so that the change amount of the exposure amount per unit time is constant.

  According to the present invention, it is possible to provide an imaging apparatus and an imaging method in which no flickering occurs even when the aperture value is changed.

1 is a block diagram mainly showing an electrical configuration of a camera according to an embodiment of the present invention. 6 is a graph showing an aperture control operation in the camera according to the embodiment of the present invention. 6 is a flowchart illustrating an exposure control operation in the camera according to the embodiment of the present invention. 6 is a flowchart illustrating an exposure control operation in the camera according to the embodiment of the present invention.

  Hereinafter, an example in which the present invention is applied to a digital camera as an embodiment will be described. This digital camera has an imaging unit, and the imaging unit converts the subject image into image data, and based on the converted image data, the subject image is displayed in live view on a display unit disposed on the back of the main body. . The photographer determines the composition and shooting timing by observing the live view display. When the moving image button or the like is operated, recording of moving image data is started, and when the moving image button or the like is operated again, recording of moving image data is ended. In addition, still images can be taken by operating the release button. Image data of still images and moving images recorded on the recording medium can be reproduced and displayed on the display unit when the reproduction mode is selected.

  In addition, the camera according to the present embodiment adjusts the exposure amount by changing the aperture amount of the aperture, and then adjusts the ISO sensitivity and the electronic shutter speed so as to match the change rate of the exposure amount according to the change of the aperture aperture. (For details, see ΔEv in FIG. 2B, see FIG. 4).

  FIG. 1 is a block diagram mainly showing an electrical configuration of the camera according to the present embodiment. This camera has a camera body 10 and a lens barrel 20 that can be attached to the camera body 10. The present embodiment is a so-called interchangeable lens camera in which the camera body 10 and the lens barrel 20 are configured separately. However, the present invention is not limited to this, and the lens barrel may be in the form of a camera integrated with the camera body.

  A control unit 11, an imaging control unit 15, an imaging element 16, and a mechanical shutter 17 are disposed in the camera body 10.

  The mechanical shutter 17 is a so-called focal plane shutter or lens shutter disposed on the front side of the image sensor 16. The mechanical shutter 17 allows the subject luminous flux from the lens barrel 20 to pass during a predetermined exposure time (determined by the shutter speed) during still image shooting. Further, the mechanical shutter 17 is in an open state during moving image shooting or live view display.

  The imaging element 16 is disposed on an extension line of the optical axis O of the optical system of the lens barrel 20. The imaging device 16 has a plurality of photoelectric conversion pixels, receives an object image (light image) formed by the lens barrel 10 on the imaging surface, photoelectrically converts the object image by each photoelectric conversion pixel, A pixel signal is generated and output to the imaging control unit 15.

  The imaging control unit 15 performs readout control of pixel signals from the imaging element 16 based on the control signal from the control unit 11. The imaging control unit 15 has an electronic shutter, and can control the exposure time (electronic shutter speed) in a plurality of photoelectric conversion pixels. In addition, ISO sensitivity can be controlled by amplifying pixel signals read from a plurality of photoelectric conversion pixels at a predetermined amplification factor. The imaging control unit 15 functions as an amplifying unit that amplifies the pixel signal generated by the imaging element with a predetermined amplification factor.

  The control unit 11 includes peripheral circuits such as a CPU (Central Processing Unit) and an ASIC (Application Specific Integrated Circuit), and controls the camera body 10 and the lens barrel 20. In particular, the CPU controls the entire camera according to a program stored in a non-volatile memory such as a flash memory. The controller 11 includes an exposure setting value calculator 12, an aperture value transmitter / receiver 13, and a shutter speed / sensitivity operation controller 14. The aperture value transmission / reception unit 13 includes a communication circuit, and each unit is executed by software by the CPU.

  The control unit 11 functions as a control unit that adjusts the exposure amount of the image data based on the pixel signal generated by the imaging device by changing the aperture of the aperture and the amplification factor of the amplification unit, and the control unit drives the aperture. Then, after adjusting the exposure by changing the aperture, the exposure is adjusted by changing the amplification factor of the amplifying means based on the change in the aperture of the diaphragm (for example, FIG. 2B and FIG. 3). S5-S9, see S11-S19 in FIG. 4). The control means changes the amplification factor of the amplification means so that the exposure amount changes at a rate that matches the change rate of the exposure amount according to the change in the aperture of the diaphragm (for example, in FIG. ΔEv from T1 to T4, see S13 to S19 in FIG. Further, when the aperture is changed by driving the aperture, the control means, for example, on the exposure control, the maximum value and the minimum value of the range in which the aperture value follows the exposure in the program diagram (hereinafter referred to as the aperture limit). When the value reaches the value, the exposure amount is adjusted by changing the amplification factor of the amplifying means (for example, at time T2 in FIG. 2B, the exposure amount is switched from the aperture value Av to the ISO sensitivity Sv until the aperture limit is reached). (See S5 Yes, S7, S9 in FIG. 3, S5 No after reaching the opening limit, S11-S19 in FIG. 4).

The control unit 11 functions as a control unit that adjusts the exposure amount of the image data based on the pixel signal generated by the imaging device by changing the aperture of the diaphragm and the electronic shutter speed of the electronic shutter speed setting unit. After adjusting the exposure amount by driving the aperture and changing the aperture, the exposure amount is adjusted by changing the electronic shutter speed of the electronic shutter speed setting means based on the change in the exposure amount due to the change in the aperture of the aperture (For example, see FIG. 2 (b), S5 to S9 in FIG. 3, S21-S27 in FIG. 4). The control means changes the electronic shutter speed of the electronic shutter speed setting means so that the exposure amount change speed matches the exposure amount change speed according to the change in aperture stop (for example, FIG. ), ΔEv at times T1 to T4, see S21 to S27 in FIG. In addition, when the aperture is reached when the aperture is changed by driving the diaphragm, the control unit adjusts the exposure amount by changing the electronic shutter speed of the electronic shutter speed setting unit (for example, FIG. ) At time T2, exposure amount adjustment switched from aperture value Av to ISO sensitivity Sv, S5 Yes, S7, S9 in FIG. 3 until reaching the opening limit, S5 No after reaching the opening limit, and S21-S27 in FIG. reference).

  An exposure set value calculation unit 12 in the control unit 11 receives a pixel signal from the imaging control unit 15, and an aperture value, a mechanical shutter speed, an electronic shutter speed, and an ISO sensitivity for obtaining appropriate exposure from subject luminance based on the pixel signal. And the like, and the aperture value transmission / reception unit 13 and the shutter speed / sensitivity operation control unit 14 are set. Further, information on the aperture value from the lens barrel 20 side is input via the aperture value transmitting / receiving unit 13. The exposure setting value calculation unit 12 functions as an electronic shutter speed setting unit that sets the electronic shutter speed of the image sensor.

  The aperture value transmission / reception unit 13 includes a communication circuit for transmitting and receiving between the camera body 10 and the lens barrel 20, and the aperture value calculated by the exposure setting value calculation unit 12 on the camera body 10 side is used as the lens barrel. This is transmitted to the 20th diaphragm operation control unit 23. In addition, the aperture value transmission / reception unit 13 is configured such that when the aperture operation control unit 23 on the lens barrel 20 side is changed to an aperture value based on the focal length (zoom encoder value) detected by the zoom position detection unit 24, The changed aperture value is received.

  The shutter speed / sensitivity operation control unit 14 inputs the electronic shutter speed and ISO sensitivity calculated by the exposure setting value calculation unit 12, and performs operation control so as to obtain the electronic shutter speed and ISO sensitivity. Further, when taking a still image, the mechanical shutter 17 is controlled so that the shutter speed calculated by the exposure setting value calculation unit 12 is obtained. At the time of moving image shooting or live view display, the mechanical shutter 17 is opened.

  In the lens barrel 20, a front group lens 21a, a rear group lens 21b, a diaphragm 22, a diaphragm operation control unit 23, a zoom position detection unit 24, a diaphragm operation unit 25, and a zoom control unit 26 are provided.

  The front group lens 21 a and the rear group lens 21 b (collectively, the photographic lens 21 or the photographic optical system) adjust the focus lens in the photographic lens 21 to adjust the subject image on the imaging surface of the image sensor 16. The focal length can be changed by adjusting the zoom lens of the photographic lens 21.

  The diaphragm 22 is disposed in the optical path of the photographing lens 21. The aperture 22 is mechanically variably driven by the aperture operating unit 21. By changing the aperture diameter, the amount of subject light incident on the image sensor 16 can be changed. That is, the diaphragm 22 functions as a diaphragm that restricts light passing through the photographing optical system.

  The zoom position detector 24 has a so-called zoom encoder, detects the position of the zoom lens in the photographing lens 21, and outputs it to the aperture operation controller 23.

  The zoom control unit 26 drives and controls the zooming lens of the photographic lens 21 in accordance with a manual operation of the photographer. The zoom control unit 26 may be of a type that is directly and manually driven by a photographer, in addition to being electrically driven and controlled by an actuator.

  As described above, the aperture operation control unit 23 controls the aperture operation unit 25 so that the aperture value input via the aperture value transmission / reception unit 13 is obtained. The aperture operation control unit 23 transmits aperture drive speed information stored in a memory in the lens barrel 20 to the control unit 11 via the aperture value transmission / reception unit 13. The aperture operation control unit 23 controls the aperture operation unit 25 so as to keep the aperture value constant according to the focal length detected by the zoom position detection unit 24.

  Next, the aperture control operation in this embodiment will be described with reference to FIG. In order to facilitate understanding of the aperture control operation in the present embodiment, first, the conventional aperture control operation will be described with reference to FIG.

  As described above, even when the lens aperture value prediction is used in moving image recording or live view display, an error occurs from the actual aperture value, and the ISO sensitivity and electronic shutter obtained by the exposure calculation based on the predicted value are generated. The change in speed and the actual aperture position do not completely coincide with each other, and an error occurs with respect to the optimum exposure. Because of this error, flickering occurs in photographing brightness when other exposures (ISO sensitivity and electronic shutter speed) are controlled simultaneously with aperture driving.

  In the example shown in FIG. 2A, the horizontal axis represents the number of frames (time), and the vertical axis represents subject luminance (Bv), electronic shutter speed (Tv), aperture value (Av), ISO sensitivity (Sv), appropriate The change in deviation (ΔEv) from exposure is shown. If the subject brightness Bv is changed from 10 to 5 at time T1, the aperture value Av is set to 9 to 6 at a low speed in consideration of the appearance of the moving image and live view display in order to maintain an appropriate exposure amount. Aperture control is performed according to the aperture drive speed, and the aperture value Av is reached at time T2. In this lens barrel 20, it is assumed that the aperture value Av is set not to be smaller than 6 due to the aperture limit. Therefore, in order to maintain an appropriate exposure amount, the ISO sensitivity Sv is changed from 5 to 7 at time T2.

  As described above, in the example shown in FIG. 2A, the aperture value Av gradually changes from time T1 to T2, and the ISO sensitivity Sv changes sharply from time T2 to T3. For this reason, the exposure follow-up speed at the times T1 to T2 and the exposure follow-up speed at the times T2 to T3 are different, and as a result, the luminance change of the image is large (see change of ΔEv in the figure). When viewed as a moving image or a live view display, the image flickers in the region 31 and looks bad.

When the shooting mode at the time of moving image recording is set to the program mode (P mode) or the shutter speed priority mode (S mode), the exposure follow-up operation is generally performed according to the following procedure.
(I) For example, there is a large change in the subject brightness Bv due to the pan / tilt operation.
(Ii) The aperture value Av is followed so that the appropriate exposure amount Ev is obtained at a slow speed.
(Iii) The aperture value Av reaches the limit (opening limit) in exposure control.
(Iv) The ISO sensitivity Sv or the electronic shutter speed Tv is changed to obtain an appropriate exposure amount Ev. In this case, Sv and Tv change rapidly.

  In the exposure follow-up operation described above, as described with reference to FIG. 2A, the ISO sensitivity or the electronic shutter speed Tv changes abruptly, so that the luminance change of the image is large and the image flickers. Therefore, in the present embodiment, the process (iv) is solved by changing the following (iv ′) (iv ″).

(Iv ′) An upper limit is set for the exposure change amount between one frame of the ISO sensitivity Sv and the electronic shutter speed Tv.
(Iv ″) The upper limit of the exposure change amount is set by the aperture driving speed information obtained from the lens barrel, and the exposure tracking speed of the ISO sensitivity Sv and the electronic shutter speed Tv is set on the extension line of the exposure tracking at the aperture value Av. Try to get on.

  FIG. 2B shows an example of aperture drive control when the above-described changes (iv ′) and (iv ″) are performed. In this example, the aperture value (Av) and the ISO sensitivity (Sv) are changed while the electronic shutter speed (Tv) remains fixed. Even when the aperture value (Av) and the electronic shutter speed (Tv) are changed while the ISO sensitivity (Sv) is fixed, the same control as in FIG. 2B is performed.

In FIG. 2B, Bv is subject luminance including a difference (ΔEv) between photographing luminance and target luminance, and Bv can be calculated from the following equation (1). Note that the photographing luminance indicates a luminance corresponding to the brightness of an image obtained when photographing with the current exposure setting. If the current exposure setting deviates from the optimal exposure setting, the obtained image will be under or over from proper exposure. The target brightness indicates a brightness corresponding to the brightness of the image obtained when the optimal exposure setting is set.
Bv = Tv + Av + Sv + ΔEv (1)

  FIG. 2B shows a case where the example of FIG. 2A is applied to the present embodiment. The lower limit value (opening limit) of the aperture value Av is 6, and the upper limit of the amount of change between one frame is 0.2.

  Also in this example, the subject brightness Bv changes from 10 to 5 at time T1, the aperture value Av changes slowly from 9 to 6, and the aperture value Av reaches 6 at time T2. In this lens barrel, since the aperture value Av does not become smaller than 6, the ISO sensitivity Sv changes from 5 to 7 at time T2 in order to maintain an appropriate exposure amount.

  In the example shown in FIG. 2A, the time from time T2 to time T3 is very short, and the ISO sensitivity Sv has changed rapidly from 5 to 7. However, in the example shown in FIG. 2B, the time from time T2 to T4 is longer than the time from T2 to T3. For this reason, the luminance change is small, and when viewed as a moving image, the image does not flicker in the region 32, and the appearance does not deteriorate.

  Furthermore, in the example shown in FIG. 2B, the change rate of the luminance difference (ΔEv) from time T1 to T2 is the same as the change rate of the luminance difference (ΔEv) from time T2 to T4. From time T1 to T4, the luminance difference ΔEv is a straight line. For this reason, since the luminance change is constant, the flicker of the image can be minimized.

  Next, the diaphragm drive operation in the present embodiment will be described using the flowcharts shown in FIGS. This flow is executed by the CPU in the control unit 10 controlling each unit in accordance with a program stored in a memory (not shown).

  When the flow shown in FIG. 3 starts, first, the subject brightness (Bv) is calculated (S1). Here, the exposure setting value calculation unit 12 inputs a pixel signal from the image sensor 16 via the imaging control unit 15, and calculates subject luminance (Bv) based on the pixel signal.

  Once the subject brightness (Bv) is calculated, aperture drive speed information is acquired from the lens (lens barrel 20), and the exposure change amount is set to the clip value (S3). Here, aperture drive speed information is acquired from the aperture operation control unit 23 in the lens barrel 20. Further, the exposure change amount is set to the clip value, that is, the upper limit of the exposure change amount is set by the aperture driving speed information acquired from the lens barrel 20. Thus, the exposure follow-up speed of the ISO sensitivity Sv and the electronic shutter speed Tv is set on the extension line of the exposure follow-up speed at the aperture value Av.

  Next, it is determined whether or not the exposure interlocking range is a range in which the aperture is moved (within the aperture limit range) (S5). Here, in order to obtain an appropriate exposure corresponding to a change in luminance of the subject, it is sufficient to change the aperture value Av, or it is necessary to change the ISO sensitivity Sv or the electronic shutter speed Tv, not just the aperture value Av. Determine whether. Since the aperture value Av is a finite range from the maximum aperture value to the maximum aperture value, depending on the change in the subject brightness, it may not be possible to obtain an appropriate exposure amount simply by changing the aperture value Av. is there.

  If the result of determination in step S5 is that the exposure interlocking range is a range for moving the iris, the ISO sensitivity Sv and the electronic shutter speed Tv are fixed (S7). In this case, the currently set Sv and Tv are fixed to obtain the appropriate exposure amount.

  Subsequently, the aperture setting value is calculated from Av = Bv− (Sv−Tv) (S9). Since Sv and Tv are fixed, the exposure setting value calculation unit 12 calculates Av as the appropriate exposure amount from these values. The calculated aperture setting value is transmitted to the lens barrel 20 via the aperture value transmission / reception unit 13, and the aperture operation control unit 23 controls the driving of the aperture 22.

  On the other hand, if the result of determination in step S5 is that the exposure interlocking range is not within the range to move the aperture, it is next determined whether or not to follow exposure with ISO sensitivity Sv (S11). For example, in the program diagram, when the Bv value is in a region where the ISO sensitivity Sv can be changed, the ISO sensitivity Sv is changed to even follow the exposure, and when the Bv value is not a region where the ISO sensitivity Sv can be changed, the electronic shutter Tv. Change the to make it follow the exposure. To follow the exposure, there are a method of following the exposure with ISO sensitivity and a method of following the exposure with the electronic shutter speed. It may be set automatically in the set shooting mode, or the photographer may set manually if there are a plurality of possible shooting modes.

  If the result of determination in step S11 is to follow exposure with Sv, the aperture value Av and the electronic shutter speed Tv are fixed (S13).

  Next, the Sv set value is calculated from Sv = Av + Tv−Bv (S15). Since Av and Tv are fixed, the exposure setting value calculation unit 12 calculates ISO sensitivity Sv that is an appropriate exposure amount from these values. The calculated ISO sensitivity value Sv is sent to the shutter speed / sensitivity operation control unit 14, and the imaging control unit 15 controls the ISO sensitivity Sv.

  Once the Sv set value is calculated, the exposure change amount clip in which the absolute value (Sv change amount) of “current frame Sv (Sv set value) −previous frame Sv” corresponds to the aperture driving speed of the lens barrel 20 is then obtained. It is determined whether the exposure change amount is equal to or greater than the value (S3) (S17). The exposure tracking is controlled over a plurality of frames until a control value is instructed for each frame read from the imaging pixel 16 and the exposure amount is changed to reach an appropriate exposure amount. In this step, when the difference between the Sv setting value in the current frame and the Sv value that was controlled in the previous frame increases, the exposure tracking by controlling the ISO sensitivity Sv is an extension line of the exposure tracking of the aperture value Av. Judgment is made to prevent it from coming off. Note that when the subject brightness (Bv) is changed due to the camera posture change or the subject moving, the absolute value (Sv change amount) of “current frame Sv−previous frame Sv” exceeds the exposure change amount clip value (S17). : Yes) is likely to occur.

  If the result of determination in step S17 is Yes, the Sv change amount is clipped to the exposure change amount clip value. That is, Sv (current frame Sv) = previous frame Sv + exposure change amount clip value is set (S19). As a result of the determination in step S17, the change of the Sv value is large, and the exposure tracking by the ISO sensitivity Sv deviates from the extension line of the exposure tracking of the aperture value Av, so that the change of the Sv value appears on the extension line of the exposure tracking. To. The calculated Sv (current frame Sv) is sent to the shutter speed / sensitivity operation control unit 14, and the ISO sensitivity is controlled by the imaging control unit 15. When Sv is in the increasing direction, the calculation is performed according to the formula described in step S19. However, when Sv is in the decreasing direction, Sv (current frame Sv) is Sv = previous frame Sv−exposure change amount clip. Calculate by value.

  If it is determined in step S11 that exposure tracking is performed at Sv, exposure tracking is performed by changing the aperture value Av until the time corresponding to time T2 in FIG. 2B (S5 in FIG. 3). When the time corresponding to time T2 has passed, exposure follow-up is performed with the Sv value calculated in step S15 or the Sv value clipped in step S19 (see S13 to S19 in FIG. 4).

  On the other hand, if the result of determination in step S11 is that exposure tracking is not performed at Sv, the process proceeds to exposure tracking at Tv, and the aperture value Av and ISO sensitivity Sv are fixed (S21).

  Next, a Tv set value is calculated from Tv = Bv + Sv−Av (S23). Since Av and Sv are fixed, from these values, the exposure setting value calculator 12 calculates Tv that is the appropriate exposure amount. The calculated Tv value is sent to the shutter speed / sensitivity operation control unit 14, and the imaging control unit 15 controls the electronic shutter speed.

  When the Tv set value is calculated, an exposure change amount clip in which the absolute value (Tv change amount) of “current frame Tv (Tv set value) −previous frame Tv” corresponds to the aperture driving speed of the lens barrel 20 is then obtained. It is determined whether the exposure change amount is equal to or greater than the value (S3) (S25). As described above, the exposure follow-up is controlled over a plurality of frames until a control value is instructed for each readout frame from the imaging pixel 16 and the exposure amount is changed to reach an appropriate exposure amount. In this step, when the difference between the Tv value in the current frame and the Tv value in the previous frame becomes large, the exposure tracking by controlling Tv is prevented from deviating from the extension line of the exposure tracking of the aperture value Av. It is judged.

  If the result of determination in step S25 is Yes, the Tv change amount is clipped to the exposure change amount clip value. That is, Tv (current frame Tv) = previous frame Tv + exposure change amount clip value is set (S27). As a result of the determination in step S25, the change in the Tv value is large, and the exposure follow-up at the electronic shutter speed Tv deviates from the extension line of the exposure follow-up of the aperture value Av, so the change in the Tv value falls on the extension line of the exposure follow-up. Like that. The calculated Tv (current frame Tv) is sent to the shutter speed / sensitivity operation control unit 14, and the imaging control unit 15 controls the electronic shutter speed. When Tv is in the increasing direction, calculation is performed using the formula described in step S27. However, when Tv is in the decreasing direction, Tv is Tv (current frame Tv) = previous frame Tv−exposure change amount clip. Calculate by value.

  If it is determined in step S11 that exposure tracking is not performed in Sv, that is, exposure tracking is performed in Tv, exposure tracking is performed by changing the aperture value Av until a time corresponding to time T2 in FIG. When the time corresponding to time T2 has passed, exposure tracking is performed with the Tv value calculated in step S23 or the Tv value clipped in step S27 (S21 to S21 in FIG. 4). (See S27).

  When the process in step S19 is performed, the determination result in step S17 is No, the process in step S27 is performed, the determination result in step S25 is No, or the process in step S9 is performed 3 and FIG. 4 are finished. When the pixel signal for one frame is read out, the processing is performed again from step S1.

  As described above, in one embodiment of the present invention, when the aperture value is changed in order to maintain the appropriate exposure amount when the subject brightness changes, the aperture is changed by driving the aperture to change the exposure amount. (For example, see S5 to S9 in FIG. 3), the exposure amount is adjusted by changing the amplification factor of the pixel signal or the electronic shutter speed based on the change in the aperture of the diaphragm (for example, FIG. 2 (b), see FIG. For this reason, it is possible to prevent the image from flickering.

  In the embodiment of the present invention, the exposure tracking can be selectively performed by the ISO sensitivity and the electronic shutter speed. However, the present invention is not limited to this, and the exposure tracking may be performed by only one of them.

  In each embodiment of the present invention, the exposure setting value calculation unit 12, the aperture value transmission / reception unit 13, and the shutter speed / sensitivity operation control unit 14 are included in the control unit 11, but are executed by the CPU in software. However, all may be configured by hardware or may be executed by software.

  In the present embodiment, the digital camera is used as the photographing device. However, the camera may be a digital single-lens reflex camera or a compact digital camera, and may be used for moving images such as video cameras and movie cameras. It may be a camera, and may be a camera built in a mobile phone, a smart phone, a personal digital assistant (PDA), a personal computer (PC), a tablet computer, a game machine, or the like. In any case, the present invention can be applied to any device for photographing that can perform exposure control using a diaphragm.

  Of the techniques described in this specification, the control mainly described in the flowchart is often settable by a program and may be stored in a recording medium or a recording unit. The recording method for the recording medium and the recording unit may be recorded at the time of product shipment, may be a distributed recording medium, or may be downloaded via the Internet.

  In addition, regarding the operation flow in the claims, the specification, and the drawings, even if it is described using words expressing the order such as “first”, “next”, etc. It does not mean that it is essential to implement in this order.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, you may delete some components of all the components shown by embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 10 ... Camera body, 11 ... Control part, 12 ... Exposure setting value calculating part, 13 ... Aperture value transmission / reception part, 14 ... Shutter speed / sensitivity operation control part, 15 ... Imaging Control unit, 16 ... imaging device, 17 ... mechanical shutter, 20 ... lens barrel, 21a ... front group lens, 21b ... rear group lens, 22 ... aperture stop, 23 ... Aperture operation control unit, 24 ... zoom position detection unit, 25 ... aperture operation unit, 26 ... zoom control unit

Claims (7)

An image sensor that captures subject light that has passed through the imaging optical system and generates a pixel signal;
A diaphragm for limiting the luminous flux that has passed through the photographing optical system;
Amplifying means for amplifying the pixel signal generated by the image sensor at a predetermined amplification rate;
Control means for adjusting an exposure amount of image data based on a pixel signal generated by the imaging device by changing an aperture of the diaphragm and an amplification factor of the amplification means;
Comprising
The control means drives the diaphragm and adjusts the exposure amount so that the amount of change in the exposure amount per unit time is constant, and then continuously adjusts the exposure amount based on the change in the aperture of the diaphragm. An image pickup apparatus characterized in that the exposure amount is adjusted by changing the amplification factor of the amplification means so that the change amount of the exposure amount per unit time is constant.   2. The control unit according to claim 1, wherein when the aperture is changed by driving the diaphragm, the amount of exposure is adjusted by changing an amplification factor of the amplifying unit when the aperture limit is reached. The imaging device described. An image sensor that captures subject light that has passed through the imaging optical system and generates a pixel signal;
A diaphragm for limiting the luminous flux that has passed through the photographing optical system;
Electronic shutter speed setting means for setting the electronic shutter speed of the image sensor;
Control means for adjusting an exposure amount of image data based on a pixel signal generated by the image pickup device by changing an aperture of the diaphragm and an electronic shutter speed of the electronic shutter speed setting means;
Comprising
The control means adjusts the exposure amount by driving the diaphragm to change the opening so that the amount of change in the exposure amount per unit time is constant, and then continuously exposing the amount of exposure due to the change in the aperture of the diaphragm. An image pickup apparatus, wherein the exposure amount is adjusted by changing the electronic shutter speed of the electronic shutter speed setting means based on the change so that the change amount of the exposure amount per unit time is constant.   The control means changes the electronic shutter speed of the electronic shutter speed setting means so that the exposure amount changes at a rate that matches the change rate of the exposure amount according to the change in the aperture of the diaphragm. The imaging device according to claim 3.   The control means adjusts the exposure amount by changing the electronic shutter speed of the electronic shutter speed setting means when the aperture limit is reached when the aperture is changed by driving the diaphragm. The imaging device according to claim 3 or 4. An image sensor that captures subject light that has passed through the imaging optical system and generates a pixel signal;
A diaphragm for limiting the luminous flux that has passed through the photographing optical system;
In an imaging method in an imaging apparatus comprising:
Amplifying the pixel signal generated by the imaging device with a predetermined amplification factor,
When adjusting the exposure amount of image data based on the pixel signal generated by the image sensor by changing the aperture of the aperture and the amplification factor, the amount of change in the exposure amount per unit time is adjusted by driving the aperture. After adjusting the amount of exposure by changing the aperture to be constant, the gain is continuously changed based on the change in the aperture of the diaphragm so that the amount of change in the amount of exposure per unit time is constant. And adjusting an exposure amount. An image sensor that captures subject light that has passed through the imaging optical system and generates a pixel signal;
A diaphragm for limiting the luminous flux that has passed through the photographing optical system;
In an imaging method in an imaging apparatus comprising:
Set the electronic shutter speed of the image sensor,
When adjusting the exposure amount of the image data based on the pixel signal generated by the image sensor by changing the aperture of the aperture and the electronic shutter speed, the amount of change in the exposure amount per unit time by driving the aperture after There was adjusted exposure amount by changing the opening to be constant, the amount of change in the exposure amount per unit time the electronic shutter speed based on the change in exposure amount due to continuous changes in the aperture of the diaphragm above An imaging method, wherein the exposure is adjusted by changing the exposure to be constant.

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