Imaging device, control method thereof, and program

Abstract

To provide an image pickup apparatus which is capable of preventing an increase in time required to reach correct exposure while suppressing deterioration of an aperture and reducing changes in the exposure of an image caused by exposure control, a control method therefor, and a program.SOLUTION: An image pickup apparatus 110 includes: an aperture control unit 116 configured to control a drive of an aperture 102; a brightness value calculation unit 113 configured to calculate a subject brightness from an image signal generated by an image pickup element 111; and an exposure control unit 114 configured to calculate a correct exposure on the basis of the subject brightness and discretely calculate a setting value of the aperture 102 on the basis of the correct exposure. The aperture control unit 116 calculates a first target value on the basis of a present value and the correct exposure of the aperture 102, and drives the aperture 102 at a first drive speed to reach the first target value and then drives the aperture at a second drive speed to the setting value. The exposure control unit 114 changes a gain to be applied to the image signal while the aperture 102 is driven from the first target value to the setting value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging apparatus, a control method thereof, and a program, and more particularly to an imaging apparatus capable of controlling an aperture, and a control method and a program thereof. [Background technology]

[0002] Conventionally, imaging devices have been provided with multiple exposure parameters, and there are technologies for maintaining the imaging device at an appropriate exposure by controlling these parameters in combination or by controlling at least one of them. Typical exposure parameters provided in imaging devices include the lens aperture value, the imaging device's shutter speed, and the digital gain applied to the captured image. Furthermore, because the aperture value is set by mechanically driving the lens aperture, it is preferable to change the aperture value setting less frequently in consideration of the aperture's durability. However, when shooting video, the aperture value setting is likely to be changed more frequently. Therefore, Patent Document 1 discloses a technology for discretely changing the aperture value in order to reduce the aperture drive frequency and reduce its deterioration.

[0003] However, the technology disclosed in Patent Document 1 does not take into consideration the fact that when the aperture value is changed discretely, the exposure conditions change significantly all at once. Here, when this technology is used when capturing still images, it is possible to adjust the imaging device to the appropriate exposure by controlling exposure parameters other than the aperture value between the time the aperture value is changed and the time the image is captured. On the other hand, when this technology is used when capturing video, since the image is captured at a constant frame rate, it is preferable that the imaging device always maintain the appropriate exposure. While it is theoretically possible to maintain the appropriate exposure of the imaging device by controlling the gain and shutter time in accordance with the aperture drive, it is not easy to perform these controls in accordance with an aperture whose aperture value is changed discretely.

[0004] In response to this, Patent Document 2 discloses a technique for gradually changing the aperture by a unit amount to mitigate the problem of large changes in exposure conditions caused by driving the aperture. Furthermore, in order to maintain the proper exposure of the imaging device, the gain is also controlled while the aperture is being driven. Thus, Patent Document 2 controls the gain while gradually driving the aperture, thereby maintaining the proper exposure of the imaging device and minimizing the impact of driving the aperture on the exposure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-19288 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-98779 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology disclosed in Patent Document 2 drives the aperture stepwise, which results in a long time until the aperture reaches the final target value. Furthermore, to maintain proper exposure in the imaging device, the gain is controlled simultaneously with the aperture drive, but if the subject is dark, a large gain must be applied. However, applying a large gain can amplify the noise components of the image, potentially impairing image quality. Therefore, it becomes necessary to set an upper limit on the gain to take noise into account while the aperture is being driven. However, setting an upper limit on the gain in this way makes it impossible to maintain proper exposure even if the gain is controlled while the aperture is being driven. Therefore, it is desirable for the aperture to reach the target value as quickly as possible.

[0007] Therefore, an object of the present invention is to provide an imaging device, a control method thereof, and a program that can prevent the time required to reach the correct exposure from increasing while suppressing aperture deterioration and reducing changes in image exposure due to exposure control. [Means for solving the problem]

[0008] In order to solve the above problem, an imaging device according to the present invention comprises an aperture control means for controlling the driving of an aperture that adjusts the amount of light, an imaging means for photoelectrically converting a light beam to generate an image signal, a brightness calculation means for calculating a subject brightness from the image signal generated by the imaging means, an appropriate exposure calculation means for calculating an appropriate exposure based on the subject brightness calculated by the brightness calculation means, a setting value calculation means for discretely calculating a setting value of the aperture based on the appropriate exposure, a first target value calculation means for calculating a first target value based on the current value of the aperture and the appropriate exposure, a second target value calculation means for calculating a second target value that is closer to the setting value than the first target value based on the current value of the aperture, the appropriate exposure and the first target value, and an exposure compensation means for changing at least one of the shutter time of the imaging means and a gain applied to the image signal while the aperture is being driven from the first target value to the second target value, wherein the aperture control means drives the aperture to the first target value at a first drive speed, and then drives it to the second target value at a second drive speed. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the time required to reach the correct exposure from becoming long while suppressing deterioration of the aperture and reducing changes in image exposure due to exposure control. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a hardware configuration of an imaging system including an imaging device according to a first embodiment of the present invention. [Figure 2] FIG. 3 is a program diagram of exposure control according to the first embodiment of the present invention. [Figure 3] 4 is a flowchart of an aperture control process according to the first embodiment of the present invention. [Figure 4] 2 is a diagram showing an example of exposure control in the first embodiment of the present invention, which is executed by an exposure control unit, an aperture control unit, and a gain control unit in FIG. 1. FIG. [Figure 5]10 is a flowchart of an aperture control process according to a second embodiment of the present invention. [Figure 6] 10A and 10B are diagrams illustrating an example of exposure control executed by an exposure control unit, an aperture control unit, and a gain control unit in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations will be omitted.

[0012] Example 1 First, an imaging system 1 including an imaging device 110 according to a first embodiment of the present invention will be described.

[0013] FIG. 1 is a block diagram showing the hardware configuration of the imaging system 1. As shown in FIG.

[0014] The imaging system 1 includes an imaging device 110 and a lens device 100 that is detachably attached to the imaging device 110. In this embodiment, the lens device 100 is detachable from the imaging device 110, but the lens device 100 may be integrated with the imaging device 110.

[0015] The imaging device 110 includes an imaging element 111, an imaging device control unit 112, and an output unit 120. The imaging device control unit 112 also includes a brightness value calculation unit 113, an exposure control unit 114, a shutter control unit 115, an aperture control unit 116, a gain control unit 117, a camera communication unit 118, and an image processing unit 119.

[0016] The lens device 100 includes a lens 101 , an aperture 102 , a lens communication unit 103 , and a lens control unit 104 .

[0017] Although only one lens is shown in FIG. 1, the lens 101 is actually made up of a group of lenses including a focus lens and a zoom lens.

[0018] The diaphragm 102 adjusts the amount of light entering through the lens 101 .

[0019] The image sensor 111 (imaging means) is, for example, a CCD or CMOS sensor, and photoelectrically converts the light beam that has passed through the lens 101 and the diaphragm 102 to generate an image signal, which is then output to the image capture device control unit 112 .

[0020] The lens communication unit 103 communicates with the image capture device 110 via the camera communication unit 118 .

[0021] The lens control unit 104 controls the lens 101 and the aperture 102 via an actuator (not shown) in the lens device 100, based on operations of an operating member (not shown) of the lens device 100 by a user and information from the imaging device 110 obtained via the lens communication unit 103. The actuator here is, for example, any one of a DC motor, a stepping motor, an ultrasonic motor, etc.

[0022] The imaging device control unit 112 is configured by a CPU.

[0023] The luminance value calculation unit 113 (luminance calculation means) calculates the luminance value of the subject from the image signal output from the imaging element 111.

[0024] The exposure control unit 114 (proper exposure calculation means) calculates the proper exposure based on the luminance value calculated by the luminance value calculation unit 113 and the luminance value at the time of proper exposure stored in a memory (not shown). Furthermore, the exposure control unit 114 calculates exposure parameters so as to achieve the calculated proper exposure based on various information related to aperture control notified from the aperture control unit 116. Specifically, in this embodiment, at least one of the aperture value, gain, and shutter time is calculated as the setting value of the exposure parameter. The luminance value at the time of proper exposure may be a range of luminance values. Furthermore, details of the various information related to aperture control notified from the aperture control unit 116 will be described later with reference to FIG. 3. The method by which the exposure control unit 114 calculates each of the above setting values ​​will be described later.

[0025] The shutter control unit 115 controls the shutter time of the image sensor 111 (charge accumulation time by the image sensor 111) so that the shutter time is the one calculated by the exposure control unit 114 or the one set by the user using a setting means (not shown).

[0026] The aperture control unit 116 (aperture control means) determines the aperture value calculated by the exposure control unit 114 or the aperture value set by the user using a setting means (not shown) as the setting value, and controls the aperture 102 to the determined setting value. In this embodiment, the aperture 102 is controlled by communicating with the lens apparatus 100 via the camera communication unit 118. However, in a configuration in which the lens apparatus 100 and the imaging device 110 are integrated, the aperture control unit 116 may control the aperture 102 without going through the camera communication unit 118. The aperture control unit 116 also notifies the exposure control unit 114 of various information related to aperture control. Details of the aperture control process executed by the aperture control unit 116 will be described later using FIG. 3.

[0027] The gain control unit 117 applies the gain calculated by the exposure control unit 114 or the gain set by the user using a setting means (not shown) to the image signal output from the image sensor 111 .

[0028] The image processing unit 119 performs image processing on the image signal output from the image sensor 111. The image processing includes, for example, gamma correction and debayer processing.

[0029] The output unit 120 outputs the image signal that has been subjected to various image processes and that is output from the imaging device control unit 112 to a display device or a recording device (not shown).

[0030] Next, a method for setting the setting values ​​set by the exposure control unit 114 will be described with reference to Fig. 2. In this embodiment, for example, a change in brightness of 1 Ev is expressed as a change in exposure by one step.

[0031] FIG. 2 is a program diagram of exposure control according to this embodiment, with the upper part showing the gain value applied to the image signal output from the image sensor 111 and the lower part showing the aperture value of the aperture 102.

[0032] The vertical axis of each of the upper and lower rows indicates the gain value expressed in dB and the aperture value expressed in F-number. In other words, the larger the gain value, the greater the amount of amplification of the image signal, and the larger the aperture value, the smaller the opening diameter of the aperture 102.

[0033] The horizontal axis indicates the points on the program diagram shown in FIG. 2, and the gain and aperture value at each point can be derived. As the subject brightness increases, the program diagram moves from point P0 toward point P3. As the subject brightness decreases, the program diagram moves from point P3 toward point P0. The exposure control unit 114 controls the gain between points P0 and P1, between P1 and P2, and between P2 and P3. In this embodiment, since increasing the gain makes noise components in the image more noticeable, the upper limit of the gain is set to G1 db in consideration of image quality.

[0034] Furthermore, the exposure control unit 114 (setting value calculation means) calculates the setting value of the aperture 102 when transitioning between the above points based on the appropriate exposure calculated from the subject brightness. For example, when the gain reaches G0 db between points P0 and P1, the exposure may be brighter than the appropriate exposure. In this case, the exposure control unit 114 controls the setting value of the aperture 102 from Fn0 to Fn1. Similarly, when the gain reaches G0 db between points P1 and P2, the exposure may be brighter than the appropriate exposure. In this case, the exposure control unit 114 controls the setting value of the aperture 102 from Fn1 to Fn2. Here, the aperture values ​​represented by the F-numbers Fn0, Fn1, and Fn2 are discrete values ​​with the same intervals between them and the minimum drive resolution of the aperture 102. For this reason, it is preferable that the interval between the two gains G0 db and G1 db be the same interval, in terms of the number of steps, as the intervals between Fn0, Fn1, and Fn2.

[0035] As described in the prior art of Patent Document 1, by moving the aperture 102 discretely in this manner, it is possible to reduce the frequency with which the aperture 102 is driven, thereby reducing deterioration of the aperture 102. Furthermore, in this embodiment, the gain or shutter is set based on the aperture drive content when driving the aperture 102 so that the exposure conditions do not change significantly all at once. Details will be described later.

[0036] Furthermore, in this embodiment, a program diagram consisting of a combination of aperture value and gain as shown in FIG. 2 is used, but such a program diagram is not necessary as long as the exposure parameters can be controlled so that the exposure conditions do not change significantly all at once. For example, a program diagram consisting of a combination of aperture value and shutter speed, or a program diagram consisting of a combination of aperture value, shutter speed, and gain, may be used. Furthermore, in this embodiment, the upper limit of gain is set to G1 db in consideration of image quality, but this is not limited to this. For example, if the subject is too dark and proper exposure cannot be obtained even by adjusting the aperture value or shutter time, the gain may be set to a high value even at the expense of image quality. This is because setting a high gain even at the expense of image quality makes it possible to at least recognize the subject.

[0037] Next, the aperture control process executed by the aperture control unit 116 will be described with reference to the flowchart in Fig. 3. This aperture control process is executed repeatedly at regular intervals by the aperture control unit 116 of the imaging device control unit 112, which is a CPU, expanding a program stored in a ROM (not shown) of the imaging device 110 into a RAM (not shown) as well.

[0038] First, in step S300, the current value of the aperture 102 is acquired. The current value of the aperture 102 is received from the lens device 100 via the camera communication unit 118. However, the current value of the aperture 102 may also be detected or held by the imaging device 110.

[0039] In step S301, the setting value of the aperture 102 calculated by the exposure control unit 114 is acquired.

[0040] In step S302, the current value of the aperture 102 acquired in step S300 is compared with the set value of the aperture 102 acquired in step S301 to determine whether it is necessary to drive the aperture 102. Specifically, if the current value of the aperture 102 and the set value of the aperture 102 match, it is determined that it is not necessary to drive the aperture 102. Note that it may also be determined that it is not necessary to drive the aperture 102 if the difference between the current value of the aperture 102 and the set value of the aperture 102 is within an arbitrary range. If it is determined that it is necessary to drive the aperture 102 as a result of this determination, the process proceeds to step S303. On the other hand, if it is determined that it is not necessary to drive the aperture 102, the process proceeds to step S317.

[0041] In step S303, it is determined whether the current setting value of the aperture 102 acquired in step S301 has changed from the previous setting value of the aperture 102 stored in a memory (not shown) at least one time before this process was executed. Specifically, as with the determination in step S302, if the previous setting value and the current setting value match or the difference is within a given range, it is determined that there has been no change. If this determination shows that the current setting value of the aperture 102 has changed from the previous setting value of the aperture 102, the process proceeds to step S304. On the other hand, if there has been no change, the process proceeds to step S310.

[0042] In step S304, a first flag is cleared. The first flag is set when the aperture 102 reaches a first target value, which will be described later.

[0043] In step S305, the number of steps from the current exposure state to the appropriate exposure is acquired from the exposure control unit 114 (appropriate exposure step acquisition means). The number of steps is calculated by comparing the luminance value calculated by the luminance value calculation unit 113 with the luminance value at the time of appropriate exposure stored in a memory (not shown). Note that the exposure control unit 114 also calculates the number of steps from the current exposure state to the appropriate exposure in the process of calculating each setting value.

[0044] In step S306, a first target value of the aperture 102 is calculated based on the current value of the aperture 102, the setting value of the aperture 102, and the number of stops until the correct exposure obtained in step S305 (first target value calculation means). Specifically, the first target value is set to a value that is the number of stops away from the current value of the aperture 102 until the correct exposure.

[0045] In step S307, a second target value for the aperture 102 is calculated based on the current value of the aperture 102, the setting value of the aperture 102, the number of stops until proper exposure, and the first target value calculated in step S306 (second target value calculation means). Specifically, the second target value is a discrete aperture value with respect to the minimum drive resolution of the aperture 102 that is closer to the setting value of the aperture 102 acquired in step S301 than the first target value. In this embodiment, a setting value is set as the second target value in step S307.

[0046] In step S308, a first drive speed is calculated for driving the diaphragm 102 to the first target value calculated in step S306. A higher first drive speed is more desirable, and the first drive speed is set to, for example, the maximum speed at which the diaphragm 102 can be driven.

[0047] In step S309, a second drive speed for driving the diaphragm 102 to the second target value calculated in step S307 is calculated.

[0048] In step S310, it is determined whether the aperture 102 has reached the first target value set in step S306. Specifically, it is determined that the aperture 102 has reached the first target value when the first flag is set, or the current value of the aperture 102 acquired in step S300 matches the first target value set in step S306, or the difference is within an arbitrary range. If the aperture 102 has reached the first target value, the process proceeds to step S311. On the other hand, if the aperture 102 has not reached the first target value, the process proceeds to step S314.

[0049] In step S311, a first flag is set. By setting the first flag here, it becomes possible to know that the aperture 102 has reached the first target value.

[0050] In step S312, the second target value calculated in step S307 is set as the target value of the aperture 102 for the lens device 100 (second drive target value setting means).

[0051] In step S313, the second drive speed calculated in step S309 is set as the drive speed when driving the diaphragm 102 of the lens apparatus 100 to the second target value set in step S312, and then the process proceeds to step S316.

[0052] In step S314, the first target value calculated in step S306 is set as the target value of the aperture 102 for the lens device 100 (first drive target value setting means).

[0053] In step S315, the first drive speed calculated in step S308 is set as the drive speed for driving the diaphragm 102 of the lens apparatus 100 to the first target value set in step S314, and then the process proceeds to step S316.

[0054] In step S316, the lens apparatus 100 is instructed to start driving the diaphragm 102. However, the lens apparatus 100 may start driving the diaphragm 102 when the target value and drive speed are set.

[0055] In step S317, various information related to aperture control is notified to the exposure control unit 114. Specifically, the various information related to aperture control includes whether the first flag is set, the current value of the aperture 102, and the target value and drive speed of the aperture 102 set for the lens apparatus 100.

[0056] In step S318, the setting value of the aperture 102 acquired in step S301 is stored in a memory (not shown), and this process ends.

[0057] Next, an example of exposure control in this embodiment, which is executed by the exposure control unit 114, the aperture control unit 116, and the gain control unit 117, will be described with reference to FIG.

[0058] In Fig. 4, the horizontal axis represents time, the left vertical axis represents the aperture value (F-number) of the aperture 102, and the right vertical axis represents the value of gain (db) applied to the image signal output from the image sensor 111. The solid line represents the trajectory showing the change over time in the aperture value of the aperture 102 controlled by the aperture control unit 116 in the aperture control process of Fig. 3, and the dashed-dotted line represents the trajectory of the gain value controlled by the gain control unit 117 during the aperture control process of Fig. 3. Times t0 to t5 are, for example, the control cycle of the image capture device control unit 112, and each process in the image capture device control unit 112 is executed at regular intervals.

[0059] 2, the aperture 102 is driven discretely (a predetermined multiple of the minimum drive resolution) relative to the minimum drive resolution of the aperture 102 (0.5 stops in terms of the number of stops). In this embodiment, the aperture 102 is driven at intervals of two stops (four times the minimum drive resolution) in terms of the number of stops, while the interval between the upper and lower limits of the gain is two stops in terms of the number of stops. During the aperture control process in FIG. 3, not only the aperture 102 but also the gain is controlled to obtain proper exposure.

[0060] At time t0, the exposure is correct, and exposure control is performed at point P1 (aperture value: Fn1, gain: G1 db) on the program diagram in FIG.

[0061] Assume that the subject brightness becomes 1.5 stops darker between time t0 and time t1. At time t1, the subject brightness becomes 1.5 stops darker, so the exposure control unit 114 calculates a setting value for proper exposure. Since the subject brightness has become 1.5 stops darker, the setting value for the aperture 102 is calculated to control the exposure so that the subject brightness becomes 1.5 stops brighter, thereby achieving proper exposure. That is, the exposure control unit 114 controls the gain to increase its value and the aperture 102 to decrease its aperture value. However, at time t1, in the program diagram of FIG. 2, the aperture 102 is Fn1, the gain is G1 db, and the gain has reached its upper limit, so the gain control unit 117 cannot increase the gain any further. Therefore, the exposure control unit 114 changes the setting value for the aperture 102 from Fn1 to Fn0, transitioning from point P1 to point P0, thereby controlling the exposure to become brighter. That is, at time t1, the exposure control unit 114 calculates the setting value (Fn0) for the aperture 102.

[0062] Meanwhile, the aperture control unit 116 controls the aperture 102 in accordance with the aperture control process of FIG. 3. At time t1, in step S302, it is determined that the aperture 102 needs to be driven, and the process proceeds to step S303. Also in step S303, it is determined that the setting value (Fn0) of the aperture 102 at the current time t1 has changed from the setting value (Fn1) at time t0, and the process proceeds to step S304. Thereafter, in steps S306 to S309, a first target value and a second target value of the aperture 102, as well as a first drive speed and a second drive speed, are calculated. In this embodiment, the first target value of the aperture 102 is a value obtained by changing the aperture 102 in the Fn0 direction by 1.5 stops from the current value Fn1. Also, the second target value of the aperture 102 is set to Fn0. For example, the first drive speed is set to the maximum speed at which the aperture 102 can be driven, and the second drive speed is set to half the first drive speed. Next, in step S310, since the aperture 102 remains at the current aperture value (Fn1), it is determined that the first target value has not been reached, and in steps S314 and S315, the lens apparatus 100 is set to the first target value as the target value of the aperture 102 and the first drive speed as the drive speed. Thereafter, in step S316, an instruction is issued to start driving the aperture 102 so that the aperture 102 is driven to the first target value at the first drive speed, and the aperture control process is terminated.

[0063] At time t2, the aperture 102 has reached the first target value (the aperture value moved 1.5 stops from Fn1 toward Fn0). In other words, at time t2, the exposure is 1.5 stops brighter than at time t1, resulting in proper exposure. However, since exposure control is performed by driving the aperture value of the aperture 102 by two stops at a time in accordance with the program diagram in Figure 2, from time t2 it is necessary to further change the aperture 102 by the remaining 0.5 stops toward Fn0.

[0064] In the periodically repeated aperture control process, when the aperture control unit 116 determines in step S310 that the aperture 102 has reached the first target value, it executes steps S311 to S313. As a result, the target value of the aperture 102 to be transmitted to the lens apparatus 100 is set to the second target value (Fn0), and the drive speed of the aperture 102 is set to the second drive speed. Then, in step S317, various information related to aperture control is notified to the exposure control unit 114. In the example of FIG. 4, the various information related to aperture control includes that the first flag is set, that the current value of the aperture 102 is the first target value, and that the target value and drive speed of the aperture 102 are the second target value and the second drive speed, respectively.

[0065] The exposure control unit 114 (exposure compensation means) calculates a gain setting value based on various information related to aperture control notified by the aperture control unit 116 in step S317. Specifically, the gain is adjusted so that proper exposure is maintained even after the aperture 102 reaches the first target value, i.e., so that the luminance change caused by the aperture 102 being controlled to open further by 0.5 stops is offset. For example, the exposure control unit 114 calculates a gradient in steps based on the current value, target value, and drive speed of the aperture 102 notified by the aperture control unit 116, and sets the gain according to the gradient calculated to offset the exposure change (luminance change) caused by the drive of the aperture 102 from time t2 onward. In the case of FIG. 4, the aperture 102 starts to be driven at the second drive speed toward the second target value from time t2 and reaches the second target value at time t5. During this time, the exposure control unit 114 adjusts the gain controlled by the gain control unit 117 to offset the luminance change caused by the drive of the aperture 102 in steps. Therefore, between times t2 and t5, the change in exposure due to the driving of the diaphragm 102 is offset by the control of the gain, making it possible to maintain the appropriate exposure. Also, between times t1 and t2, the diaphragm 102 is driven at the highest speed toward the first target value, so the appropriate exposure is reached in a short time.

[0066] 4, the exposure control unit 114 calculates the gain setting value based on the various information related to aperture control notified from the aperture control unit 116 in step S317, but is not limited to this as long as it is a setting value of an exposure parameter other than the aperture value. For example, the exposure control unit 114 may calculate the shutter time of the image sensor 111 based on the various information related to aperture control notified from the aperture control unit 116 in step S317.

[0067] As described above, in this embodiment, when performing exposure control, the aperture 102 is driven by calculating a setting value in two-step increments. This reduces the frequency with which the aperture 102 is driven and prevents deterioration. Furthermore, when driving the aperture 102 to the setting value, it is driven at a high first drive speed up to the aperture value (first target value) that provides proper exposure. This allows proper exposure to be achieved in a relatively short time. Furthermore, when driving the aperture 102 the rest of the way to the setting value (second target value), it is driven at a second drive speed that is slower than the first drive speed, while offsetting changes in exposure due to driving of the aperture 102 by controlling the gain or shutter. This makes it possible to maintain proper exposure even when the aperture 102 reaches the setting value. Therefore, it is possible to simultaneously achieve three goals: reduced deterioration of the aperture 102, reduced changes in image exposure due to exposure control, and shorter time required to reach proper exposure.

[0068] In addition, in this embodiment, the first drive speed is the maximum speed at which the aperture 102 can be driven, and the second drive speed is half the first drive speed, but this is not limiting as long as the first drive speed is set to a speed higher than the second drive speed. For example, the effects of the present invention can be obtained even if the second drive speed is set to the minimum speed at which the aperture 102 can be driven.

[0069] Furthermore, in this embodiment, when exposure control is performed, the aperture control process (FIG. 3) is always performed, in which the aperture 102 is moved discretely and two target values ​​for the aperture 102 are set. However, predetermined shooting conditions for performing the aperture control process may also be set. For example, if the aperture 102 is driven frequently (above a predetermined frequency) in the imaging system 1, it may be determined that the predetermined shooting conditions exist, and the aperture control process may be performed. Furthermore, if the durability of the aperture 102 of the lens apparatus 100 is not high (does not have durability above a predetermined level), it may be determined that the predetermined shooting conditions exist, and the aperture control process may be performed.

[0070] Example 2 A second embodiment of the present invention differs from the first embodiment in the method of setting the first target value of the aperture 102. In the first embodiment, the first target value of the aperture 102 is set to a value that is the number of stops (1.5 stops in the example of FIG. 4 ) away from the current value of the aperture 102 to the correct exposure. However, depending on the minimum drive resolution of the aperture 102, it may not be possible to set a value that is the number of stops away from the current value to the correct exposure as the first target value. In other words, there may be cases where the number of stops from the current value of the aperture 102 to the correct exposure is not a multiple of the minimum drive resolution of the aperture 102. In this embodiment, aperture control processing in such cases will be described. Below, parts that differ from the first embodiment will be described, and the same configurations and processing as those in the first embodiment will be assigned the same reference numerals, and redundant description will be omitted.

[0071] The aperture control process in this embodiment, which is executed by the aperture control unit 116, will be described using the flowchart in Fig. 5. The flowchart in Fig. 5 differs from the flowchart in Fig. 3 in that step S500 is present between step S301 and step S302, and in that steps S501 and S502 are present instead of steps S306 and S307.

[0072] Below, steps S500 to S503 in the flowchart of FIG. 5 that are different from the flowchart of FIG. 3 will be described.

[0073] In step S500, the minimum drive resolution of the aperture 102 is acquired. The minimum drive resolution may be acquired when the lens device 100 is attached to the image capture device 110 and the lens communication unit 103 and the camera communication unit 118 start communication, or may be stored in advance in a memory (not shown) of the image capture device 110.

[0074] In step S501, a first target value of the aperture 102 is calculated based on the current value and setting value of the aperture 102, the number of stops until the correct exposure is reached, and the minimum drive resolution of the aperture 102. A detailed method for calculating the first target value in step S501 will be described later.

[0075] In step S502, a second target value of the aperture 102 is calculated based on the current value and setting value of the aperture 102, the number of stops until the correct exposure is reached, the first target value, and the minimum drive resolution of the aperture 102. For example, the second target value is the setting value of the aperture 102 acquired in step S301.

[0076] Next, a method for calculating the first target value in step S501 and the operations of the exposure control unit 114, aperture control unit 116, and gain control unit 117 in this embodiment will be described with reference to FIG.

[0077] 6, similar to FIG. 4, the horizontal axis indicates time, the left vertical axis indicates the aperture value (F-number) of the aperture 102, and the right vertical axis indicates the value of gain (db) applied to the image signal output from the image sensor 111. The solid line indicates the trajectory of the change over time in the aperture value of the aperture 102 controlled by the aperture control unit 116 in the aperture control process of FIG. 5, and the dashed-dotted line indicates the trajectory of the gain value controlled by the gain control unit 117 during the aperture control process of FIG. 5. Times t0 to t5 are, for example, the control cycle of the image capture device control unit 112, and each process within the image capture device control unit 112 is executed at regular intervals. It should be noted that the minimum drive resolution of the aperture 102 in this embodiment is 0.5 stops.

[0078] 2, the aperture 102 is driven discretely at intervals of two steps in step number conversion. Also, like in the first embodiment, the interval between the upper and lower limits of the gain is set to two steps in step number conversion.

[0079] At time t0, the exposure is correct, and exposure control is performed at point P1 (aperture value: Fn1, gain: G1 db) on the program diagram in FIG.

[0080] Assume that the subject brightness becomes 0.6 stops darker between time t0 and time t1. At time t1, the subject brightness becomes 0.6 stops darker, so the exposure control unit 114 calculates a setting value for proper exposure. In this case, the subject brightness has become 0.6 stops darker, so the setting value for the aperture 102 is calculated to control the exposure so that the subject brightness becomes 0.6 stops brighter, thereby achieving proper exposure. In other words, the exposure control unit 114 controls the gain to increase its value and the aperture 102 to decrease its aperture value. However, at time t1, in the program diagram of FIG. 2, the aperture 102 is Fn1, the gain is G1 db, and the gain has reached its upper limit, so the gain control unit 117 cannot increase the gain any further. Therefore, the exposure control unit 114 changes the setting value for the aperture 102 from Fn1 to Fn0, and controls the exposure to become brighter by transitioning from point P0 to point P1. That is, at time t1, the exposure control unit 114 calculates the setting value (Fn0) of the aperture 102.

[0081] Meanwhile, the aperture control unit 116 controls the aperture 102 according to the aperture control process of FIG. 5. In steps S501, S502, S308, and S309, a first target value, a second target value, a first drive speed, and a second drive speed of the aperture 102 are calculated. Ideally, the first target value of the aperture 102 would be a value obtained by shifting the aperture 102 0.6 stops from the current value, Fn1, toward Fn0. However, because the minimum drive resolution of the aperture 102 is 0.5 stops, it is not possible to drive the aperture 102 by 0.6 stops. Therefore, the first target value of the aperture 102 is set to the maximum value to which the aperture 102 can be driven between the current value and the correct exposure (0.6 stops in this case). In this embodiment, the first target value of the aperture 102 is a value obtained by shifting the aperture 102 0.5 stops from Fn1 toward Fn0. The second target value, first drive speed, and second drive speed of the aperture 102 are the same as those in the first embodiment. Next, in step S310, since the aperture 102 remains at the current aperture value (Fn1), it is determined that the first target value has not been reached. Therefore, as in the first embodiment, the process proceeds to steps S314 and S315, where the lens apparatus 100 is set to the first target value as the target value of the aperture 102 and the first drive speed as the drive speed. Thereafter, in step S316, an instruction is issued to start driving the aperture 102 so that the aperture 102 is driven to the first target value at the first drive speed, and the aperture control process ends.

[0082] At time t2, the aperture 102 has reached the first target value (the aperture value moved 0.5 stops from Fn1 toward Fn0). Therefore, at time t2, the exposure is 0.5 stops brighter than at time t1, but 0.1 stops darker than the appropriate exposure. However, since exposure control is performed by driving the aperture value of the aperture 102 by two stops at a time in accordance with the program diagram in FIG. 2, from time t2 it is necessary to further change the aperture 102 by the remaining 1.5 stops toward Fn0.

[0083] In the periodically repeated aperture control process, when it is determined in step S310 that the aperture 102 has reached the first target value, the aperture control unit 116 executes steps S311 to S313, S316, and S317 in the same manner as in the first embodiment.

[0084] The exposure control unit 114 calculates a gain setting value based on various information related to aperture control notified to the aperture control unit 116 in step S317. Specifically, the gain is adjusted so that proper exposure is maintained even after the aperture 102 reaches the first target value, i.e., so that the brightness change caused by the aperture 102 being controlled to open further by 1.5 stops is offset. For example, the exposure control unit 114 first calculates a gradient in steps based on the current value, target value, and drive speed of the aperture 102 notified by the aperture control unit 116, and then sets the gain to offset the exposure change (brightness change) caused by the drive of the aperture 102 from time t2 onward according to the gradient. In the example of FIG. 6, the exposure is 0.1 stops darker than the proper exposure at time t2, and the aperture 102 is driven the remaining 1.5 stops over the time from time t2 to time t6. In other words, it can be calculated that the aperture 102 moves 0.3 stops between time t2 and time t3. Therefore, if the gain is not set, the exposure will exceed the proper exposure by 0.2 stops and become brighter at time t3. Therefore, at time t2, the gain control unit 117 is controlled so that the gain is changed by 0.2 steps toward darker images at time t3.

[0085] Next, at time t3, the exposure is adjusted to the correct exposure by taking into account the exposure state at time t2, the exposure change due to the aperture 102 from time t2, and the gain change that takes these factors into consideration. Since the aperture 102 continues to be driven by the remaining 1.2 stops after time t3, the gain is set to maintain the correct exposure while taking into account the drive of the aperture 102, as in the first embodiment. Therefore, the change in exposure is offset between times t3 and t6, making it possible to maintain the correct exposure. Furthermore, taking into account the minimum drive resolution of the aperture 102, the first target value is set to an aperture value that is 0.5 stops short of the 0.6 stops that are the number of stops required to reach the correct exposure at time t1, and the drive speed is driven at the first drive speed, thereby making it possible to reach the correct exposure in a relatively short time.

[0086] As described above, in this embodiment, unlike Example 1, it is possible to reach the appropriate exposure in a relatively short time even when the minimum drive resolution of the aperture 102 does not allow the aperture 102 to be changed to a value that is the number of steps away from the current value to the appropriate exposure. Therefore, it is possible to simultaneously achieve three things: reduction in deterioration of the aperture 102, reduction in image exposure changes due to exposure control, and shortening the time required to reach the appropriate exposure, regardless of the value of the minimum drive resolution of the aperture 102.

[0087] Although the present invention has been described in detail above based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the gist of the present invention are also included in the present invention. Parts of the above-described embodiments may be combined as appropriate.

[0088] This embodiment can also be realized by providing a program that implements one or more functions to a computer in a system or device via a network or storage medium, and having a system controller in the system or device read and execute the program. The system controller may have one or more processors or circuits, and may include multiple separate system controllers or a network of multiple separate processors or circuits to read and execute the executable instructions.

[0089] The processor or circuitry may include a central processing unit (CPU), a microprocessing unit (MPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a data flow processor (DFP), or a neural processing unit (NPU).

[0090] Therefore, the program code itself that is supplied to and installed on a computer to realize the functional processing of the present invention also realizes the present invention. In other words, the computer program itself for realizing the functional processing of the present invention is also included in the present invention.

[0091] In this case, as long as it has the functionality of a program, the form of the program does not matter, such as object code, a program executed by an interpreter, or script data supplied to an OS.

[0092] The recording medium for supplying the program may be, for example, a hard disk, a magnetic recording medium such as a magnetic tape, an optical / magneto-optical storage medium, or a non-volatile semiconductor memory.

[0093] Another method of supplying the program is to store the computer program forming the present invention in a server on a computer network, and have connected client computers download and program the computer program. [Explanation of symbols]

[0094] 100 Lens device 102 aperture 103 Lens Communication Department 104 Lens control unit 110 Imaging device 112 Imaging device control section 114 Exposure control unit 116 Aperture control section 117 Gain control section 118 Camera Communication Unit

Claims

1. Aperture control means for controlling the driving of a diaphragm for adjusting the amount of light; an imaging means for photoelectrically converting the light beam to generate an image signal; a brightness calculation means for calculating a subject brightness from an image signal generated by the imaging means; an appropriate exposure calculation means for calculating an appropriate exposure based on the subject luminance calculated by the luminance calculation means; a setting value calculation means for discretely calculating the setting value of the aperture based on the appropriate exposure; a first target value calculation means for calculating a first target value based on the current aperture value and the appropriate exposure; a second target value calculation means for calculating a second target value closer to the set value than the first target value based on the current aperture value, the appropriate exposure, and the first target value; an exposure compensation unit that changes at least one of a shutter time of the image capturing unit and a gain applied to the image signal while the aperture is being driven from the first target value to the second target value; Equipped with The imaging device, wherein the aperture control means drives the aperture to the first target value at a first drive speed, and then drives the aperture to the second target value at a second drive speed.

2. 2. The image pickup apparatus according to claim 1, wherein the first target value calculation means sets the first target value within a range between the current value of the aperture and the set value.

3. 3. The imaging apparatus according to claim 1, wherein the second target value calculation means sets the second target value to the setting value.

4. The imaging device according to any one of claims 1 to 3, characterized in that the exposure compensation means changes at least one of the shutter time and the gain so as to achieve the correct exposure while the aperture is being driven from the first target value to the second target value by the aperture control means.

5. 2. The imaging device according to claim 1, wherein the second driving speed is lower than the first driving speed.

6. 6. The imaging device according to claim 1, wherein the first target value calculation means sets the first target value to a discrete aperture value with respect to a minimum drive resolution of the aperture.

7. further comprising an appropriate exposure step number acquiring means for acquiring the number of steps from the current exposure state to the appropriate exposure; 7. The imaging device according to claim 6, wherein the first target value calculation means sets the first target value to a value that is the number of stops away from the current aperture value acquired by the appropriate exposure stop acquisition means.

8. The imaging device described in claim 7, characterized in that, when the number of steps acquired by the appropriate exposure step acquisition means is not a multiple of the minimum driving resolution of the aperture, the first target value calculation means sets the first target value to the maximum aperture value that can be changed when the aperture is driven at the minimum driving resolution within a range that does not exceed the number of steps acquired by the appropriate exposure step acquisition means.

9. 9. The imaging device according to claim 1, wherein the second target value calculation means sets the second target value to a discrete aperture value with respect to a minimum drive resolution of the aperture.

10. 10. The imaging device according to claim 1, wherein the aperture control means drives the aperture to the first target value at the first drive speed and then to the second target value at the second drive speed only when the shooting conditions are predetermined shooting conditions.

11. 11. The image pickup apparatus according to claim 10, wherein the predetermined photographing condition is that the frequency of driving the diaphragm is equal to or greater than a predetermined frequency.

12. 11. The imaging apparatus according to claim 10, wherein the predetermined photographing condition is a condition in which the diaphragm does not have a durability equal to or greater than a predetermined value.

13. A control method for an imaging device, comprising: an aperture control step for controlling the driving of an aperture that adjusts the amount of light; an imaging step of photoelectrically converting the light beam to generate an image signal; a brightness calculation step of calculating a subject brightness from the image signal generated in the imaging step; an appropriate exposure calculation step of calculating an appropriate exposure based on the subject luminance calculated in the luminance calculation step; a setting value calculation step of discretely calculating the aperture setting value based on the appropriate exposure; a first target value calculation step of calculating a first target value based on the current aperture value and the appropriate exposure; a second target value calculation step of calculating a second target value that is closer to the set value than the first target value based on the current aperture value, the appropriate exposure, and the first target value; an exposure compensation step of changing at least one of a shutter time and a gain applied to the image signal in the imaging step while the aperture is being driven from the first target value to the second target value; and a control method characterized in that, in the aperture control step, the aperture is driven to the first target value at a first drive speed, and then driven to the second target value at a second drive speed.

14. A program for causing a computer to function as each of the means of the imaging device according to any one of claims 1 to 12.

Images