Imaging device, its control method, and program

Abstract

To reduce unevenness caused by flicker in an image independent of a light source.SOLUTION: An imaging apparatus has determination means that determines a first shutter speed based on the inverse of the light quantity change frequency of detected flicker, and selection means that selects a second shutter speed as a candidate in picking up an image of a subject while reducing the influence of the flicker. When a third shutter speed is set in advance in the imaging apparatus, the determination means determines, from among shutter speeds being integral multiple of the shutter speed that is the inverse of the light quantity change frequency of the detected flicker, a shutter speed closer to the third shutter speed than the other shutter speeds as the first shutter speed. The selection means selects, from among the shutter speeds that can be set in the imaging apparatus, a shutter speed with a smaller difference from the first shutter speed than the other shutter speeds as the second shutter speed.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an imaging device, a control method thereof, and a program, and particularly to a technique for calculating characteristics related to periodic light amount changes (referred to as flicker) of a subject.

Background Art

[0002] In recent years, the sensitivity of image sensors equipped in imaging devices such as digital cameras and mobile phones has been increasing. Therefore, it has become possible to obtain bright images with suppressed subject blur by setting a high shutter speed (short exposure time) to image a subject even in a relatively dark environment like indoors compared to outdoors during the day.

[0003] In addition, it is known that fluorescent lamps, which are widespread as indoor light sources, cause flicker, a phenomenon in which the light amount of a subject image changes periodically due to the influence of the commercial power frequency. When imaging a subject with a high shutter speed set under a light source where such flicker occurs, there is a risk of exposure unevenness or color unevenness occurring within one image (screen), or variation in exposure or color temperature occurring between a plurality of images obtained by continuous shooting.

[0004] In Patent Document , a technique for detecting flicker based on a plurality of images continuously acquired at a rate that is the least common multiple of the frequencies of flicker (100 Hz and 120 Hz) caused by two commercial power frequencies of 50 Hz and 60 Hz has been proposed

Prior Art Documents

Patent Documents

[0005]

Patent Document

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, the use of light-emitting diodes (LEDs) as light sources has been increasing. LEDs differ from fluorescent lamps in their method of supplying current; they control the drive current with a rectifier circuit. Therefore, the light intensity changes with a different period and waveform than the frequency of the commercial power supply. Consequently, flicker occurs under LED light sources as well as under fluorescent light sources, but the frequency of the light intensity change of the flicker is different from that of fluorescent lamps and other light sources.

[0007] Patent Document 1 discloses a method for detecting flicker under light sources such as fluorescent lamps and for the imaging device to automatically reduce the flicker effect during imaging, but it does not mention how to deal with flicker that occurs under LED light sources.

[0008] The objective of this invention is to reduce flicker-induced unevenness in images by performing imaging that reduces the effects of flicker regardless of the light source. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides an imaging device equipped with an image sensor, comprising: a flicker detection means for detecting flicker, which is a periodic change in the amount of light of a subject; and based on the frequency of the change in the amount of light of the flicker detected by the flicker detection means candidate A means for determining the shutter speed and , a means of disseminating information and , has, In the state where a preset shutter speed has been set in advance from among the settable shutter speeds in the aforementioned imaging device, The aforementioned notification means is, If the preset shutter speed does not match any of the shutter speeds that are integer multiples of the reciprocal of the flicker light intensity change frequency detected by the flicker detection means, the system provides information to the user to select whether to change to the candidate shutter speed, and the candidate shutter speed is the closest settable shutter speed to the shutter speed that is the closest integer multiple of the preset shutter speed. It is characterized by the following: [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce unevenness caused by flicker in an image, regardless of the light source. [Brief explanation of the drawing]

[0011] [Figure 1]This is a block diagram illustrating the configuration of a camera body 100, a lens unit 200, and a light-emitting device 300, which are embodiments of an imaging device implementing the present invention. [Figure 2] This figure illustrates an example of a shutter speed setting (index) table according to the present invention. [Figure 3] This is a flowchart showing the flicker reduction process according to the first embodiment of the present invention. [Figure 4] This is a flowchart relating to the flicker detection process according to the first embodiment of the present invention. [Figure 5] This figure illustrates an exemplary method for selecting multiple imaging periods when detecting flicker according to the first embodiment of the present invention. [Figure 6] This figure illustrates a modified example of the method for selecting multiple imaging periods when detecting flicker according to the first embodiment of the present invention. [Figure 7] This diagram (graph) illustrates the relationship between the method for determining each imaging period for flicker detection according to this embodiment and the number of imaging periods. [Figure 8] This diagram illustrates the luminance change based on images continuously obtained using a global shutter system. [Figure 9] This figure exemplifies the change in brightness based on images continuously obtained using a rolling shutter method. [Figure 10] This figure illustrates, as an example, the exposure time (shutter speed) setting values ​​in a first pattern of multiple imaging cycles for flicker detection according to the first embodiment of the present invention. [Figure 11] This figure illustrates, as an example, the exposure time (shutter speed) setting values ​​in a second pattern of multiple imaging cycles for flicker detection according to the first embodiment of the present invention. [Figure 12] This is a flowchart relating to the exposure time determination process for flicker reduction according to the first embodiment of the present invention. [Figure 13]This is a diagram exemplarily explaining a method for setting an ideal flicker reduction exposure time when a flicker that changes at a predetermined light amount change frequency according to the present invention occurs. [Figure 14] This is a flowchart related to shutter speed selection processing according to the first embodiment of the present invention. [Figure 15] This is a diagram exemplarily explaining the relative relationship between the shutter speed selected by the shutter speed selection processing according to the first embodiment of the present invention and the ideal shutter speed for reducing the influence of flicker. [Figure 16] This is a diagram exemplarily explaining the notification image displayed on the display unit 102 by the display processing according to the first embodiment of the present invention. [Figure 17] This is a diagram exemplarily explaining the notification image when no flicker is detected by the display processing according to the first embodiment of the invention. [Figure 18] This is a diagram exemplarily explaining the notification image displayed on the display unit 102 by the display processing according to the second embodiment of the present invention. [Figure 19] This is a diagram exemplarily explaining the transition screen to the flicker reduction processing during live view display according to the third embodiment of the present invention.

Mode for Carrying Out the Invention

[0012] (First Embodiment) (Basic Configuration of Imaging Apparatus) Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a block diagram for explaining the configurations of a camera body 100, a lens unit 200, and a light emitting device 300, which are embodiments of an imaging apparatus implementing the present invention. Note that one or more of the functional blocks shown in FIG. 1 may be realized by hardware such as an ASIC or a programmable logic array (PLA). Further, it may be realized by a programmable processor (microprocessor, microcomputer) such as a CPU or MPU executing software. Further, it may be realized by a combination of software and hardware. Therefore, even if different functional blocks are described as the main operating entities in the following explanation, the same hardware can be the main implementing entity.

[0013] First, let's explain the various parts that make up the camera body 100. The camera body 100 is equipped with a frame memory (not shown), which functions as a memory unit that can temporarily store signals (video signals) and read them out when needed. Generally, frame memory is also called RAM, and in recent years, DDR3-SDRAM (DUAL DATA RATE 3 - SYNCHRONOUS DYNAMIC RAM) is often used. Various processing becomes possible by using this frame memory.

[0014] The image sensor 101 is an imaging means that uses a charge-accumulating solid-state image sensor such as a CMOS or CCD, which can receive the light beam of a subject guided into the camera body 100 via the lens unit 200 and convert it into an electrical image signal. The image (signal) obtained using the image sensor 101 through drive control by the CPU 103, described later, is handled as various image signals such as live view display, flicker detection, and recorded images. Since the electrical signal obtained by the image sensor 101 is an analog value, it also has a function to convert it to a digital value. Furthermore, an evaluation value (photometric value) related to the brightness of the subject can be detected based on the image signal output from the image sensor 101. In addition, the exposure time of the image sensor 101 can be controlled according to the shutter speed, which can be set as an exposure control value related to the image sensor 101.

[0015] The mechanical shutter 104 is an oblique light means that can travel in a direction parallel to the signal scanning direction of the image sensor 101. The exposure time of the image sensor 101 can be controlled by adjusting the exposure aperture formed by the multiple shutter blades of the mechanical shutter according to the shutter speed described above. The adjustment of the exposure time according to the present invention can be achieved by using or using in combination the so-called electronic shutter, which is achieved by adjusting the signal reset and readout timing of the image sensor 101, and the mechanical shutter 104.

[0016] The display unit 102 is a display device that can be viewed by the user, allowing them to check the operating status of the camera body 100. For example, the display unit 102 displays images processed based on the image signal of the subject, or setting menus. The display element of the display unit 102 uses a TFT (thin film transmitter) liquid crystal. However, an LCD (liquid crystal display) or organic EL (organic electroluminescence) may also be used as the display unit 102. By displaying the image acquired by the image sensor 101 and setting conditions such as exposure control values ​​on the display unit 102 in real time while capturing the subject, it is possible to perform so-called live view display. In this embodiment, the display unit 102 is equipped with a resistive or capacitive thin-film element called a touch panel, and also serves as an operation unit that the user can operate by touch.

[0017] The CPU 103 is a control means capable of comprehensively controlling the camera body 100 and the accessories attached to the camera body 100. The CPU 103 is connected to ROM (READ ONLY MEMORY) and RAM (RANDOM ACCESS MEMORY). ROM (not shown) is a non-volatile recording element that stores programs for operating the CPU 103 and various adjustment parameters. Programs read from ROM are loaded into volatile RAM (not shown) and executed. Generally, RAM uses slower, lower-capacity elements compared to frame memory (not shown).

[0018] Next, the details of the lens unit 200 will be described. The lens unit 200 is an accessory that can be attached to the camera body 100 and is a so-called interchangeable lens equipped with a lens group 201, including a focus lens, a zoom lens, and a shift lens. For example, the focusing lens in the lens group 201 can adjust the focus on the subject by adjusting the lens position in the direction of the optical axis of the lens.

[0019] The aperture 202 is a light intensity adjustment member for adjusting the amount of light related to the light beam of a subject guided into the camera body 100 via the lens unit 200. In this embodiment, the amount of light can be adjusted by adjusting the aperture diameter of the aperture 202, and this is achieved by changing the aperture value as an exposure control value related to the aperture diameter.

[0020] The LPU203 is a control means for controlling various parts of the lens unit 200, and can, for example, control the drive of the lens group 201 and the aperture 202. The LPU203 is connected to the CPU 103 of the camera body 100 via a group of terminals (not shown), and can drive various parts of the lens unit 200 in response to control instructions from the CPU 103.

[0021] Next, the details of the light-emitting device 300 will be described. The light-emitting device 300 is an external light-emitting device that can be attached to and detached from the camera body 100 via a connection part (not shown) provided on the camera body 100. The SPU 301 is a control means that controls each part of the light-emitting device 300, and is mainly capable of controlling the light emission and communication with the camera body 100. The SPU 301 is connected to the CPU 103 of the camera body 100 via a group of contacts (not shown), and can drive each part of the light-emitting device 300 in response to control instructions from the CPU 103.

[0022] Although the various parts of the imaging device according to the first embodiment of the present invention have been described above, the present invention is not limited to the above-described configuration. For example, the camera body 100 may have a configuration that incorporates devices corresponding to the lens unit 200 and the light-emitting device 300.

[0023] (How to set the shutter speed) Next, using Figure 2, we will specifically explain how to set the shutter speed, which is an exposure control value for controlling the exposure time of the image sensor 101 according to this embodiment. Figure 2 is a diagram illustrating an example of the shutter speed setting (index) table according to the present invention.

[0024] Generally, it is known that shutter speed can be changed in increments of 1 / 2 or 1 / 3 of a stop of light intensity. However, in this embodiment, in order to address the flicker that occurs under LED light sources that periodically flicker at various frequencies, the shutter speed can be adjusted in finer increments. Specifically, in this embodiment, the shutter speed can be adjusted in increments of 1 / 4 stop from 1 / 8192.0 to 1 / 4871.0, and in increments of 1 / 8 stop from 1 / 4096.0 to 1 / 2233.4. Furthermore, the shutter speed can be set in increments of 1 / 16 stop from 1 / 2048.0 to 1 / 1069.3, and in increments of 1 / 32 stop from 1 / 1024.0 to 1 / 523.2. In addition, the shutter speed can be adjusted in increments of 1 / 64 stop from 1 / 512.0 to 1 / 258.8, in increments of 1 / 128 stop from 1 / 256.0 to 1 / 128.7, and in increments of 1 / 256 stop from 1 / 128.0 to 1 / 50.0.

[0025] Note that in the table shown in Figure 2, some shutter speeds have been omitted for readability. Furthermore, the index values ​​in the table shown in Figure 2 are used in the shutter speed selection process to reduce flicker, which will be described later.

[0026] Furthermore, the camera body 100 according to this embodiment prioritizes the use of the electronic shutter in order to allow users to freely set shutter speeds ranging from high speeds shorter than 1 / 8000 second as described above to slower shutter speeds longer than 1 / 50 second (not shown). The shutter method (use of the electronic shutter and mechanical shutter 104 individually or in combination) can be changed at any time by the user, for example, through manual operation via the menu screen displayed on the display unit 102.

[0027] (Flicker reduction processing) Next, the flicker reduction process according to this embodiment will be explained with reference to the flowchart shown in Figure 3. Figure 3 is a flowchart of the flicker reduction process according to the first embodiment of the present invention.

[0028] First, flicker reduction processing is initiated in response to a predetermined operation, such as manual operation by the user based on a menu displayed on the display unit 102 or the like. In this embodiment, the flicker reduction processing is a process that controls the display to prevent unevenness caused by flicker from occurring in moving images such as live view displays by setting a shutter speed (i.e., exposure time) that reduces the effect of the detected flicker. The flicker reduction processing according to the present invention is not limited to this, and for example, in addition to adjusting the shutter speed, a configuration that applies a gain to the image to reduce unevenness may also be used as a method for reducing flicker.

[0029] When the flicker reduction process is started, in step S301 the CPU 103 repeats the process in S301 until the flicker detection process (detection process) is started. If it is determined in step S301 that detection has started, in step S302 the CPU 103 executes the flicker detection process. Details of the flicker detection process will be described later.

[0030] Next, in step S303, the CPU 103 determines whether or not flicker is occurring based on the processing result of step S302. If it is determined in step S303 that flicker has been detected, the process proceeds to step S304; otherwise, the process proceeds to step 306. Flicker detection is defined as the occurrence of flicker above a predetermined level. The method for calculating the flicker level will be described later.

[0031] In step S304, the CPU 103 determines an exposure time (shutter speed) that reduces the effect of the previously detected flicker (flicker reduction exposure time determination process). Details of the flicker reduction exposure time determination process will be described later.

[0032] Next, in step S305, the CPU 103 performs a shutter speed selection process to select an arbitrary shutter speed capable of reducing the effects of flicker, based on the information regarding the exposure time suitable for reducing flicker, which was determined in step S304. Details of this shutter speed selection process will be described later.

[0033] In step S306, the CPU 103 performs a display process that shows the results of the processing in steps S304 and S305, including the flicker detection result (whether or not flicker was detected) and selectable values ​​for shutter speeds that can reduce the effects of flicker. Details of this display process will be described later. Through the flicker reduction process described above, an image with reduced flicker effects can be obtained regardless of the flicker frequency, and image display and recording based on this image become possible.

[0034] (Flicker detection process) Next, with reference to Figure 4, the flicker detection process (flicker detection processing) according to this embodiment will be described. As mentioned above, unlike light sources such as fluorescent lamps, LED light sources control the drive current with a rectifier circuit, so changes in light intensity (flickering), i.e., flicker, occur at a period different from the power supply frequency used to drive the light source. Therefore, when detecting flicker caused by light sources such as LEDs, it is not possible to narrow down the frequency to be detected to a specific value, as is the case with the drive power supply frequency, so it is necessary to analyze whether or not flicker occurs over a wide range of frequencies.

[0035] On the other hand, when the frequency of the flicker's light intensity change (the blinking period of the light source) matches or is an integer multiple of the imaging period when continuously imaging a subject (hereinafter referred to as synchronization), changes in light intensity (blinking) between continuously obtained images are suppressed. In this case, for example, in live view display where images are displayed continuously, no degradation in image quality such as unevenness caused by flicker occurs, but still images acquired by imaging at an arbitrary shutter speed may have exposure unevenness caused by flicker. Furthermore, even if the imaging frame rate for live view display images matches the frequency of the flicker's light intensity change, if video for recording is acquired at a different frame rate, there is a risk that the video may have exposure unevenness or brightness fluctuations caused by flicker.

[0036] Here, a known method for identifying the frequency of light intensity changes in flicker is to detect and compare the difference in light intensity (brightness and darkness) in images obtained by continuous imaging. Therefore, when using this method to identify the frequency of light intensity changes in flicker, it is necessary to adjust the imaging period (frame rate) so that it does not synchronize with the frequency of light intensity changes in flicker.

[0037] Therefore, in this embodiment, the presence or absence of flicker is detected by analyzing the frequency of the flicker's light intensity change over multiple imaging cycles. By analyzing the flicker's light intensity change frequency over multiple frequencies, it is possible to avoid the synchronization of the flicker's light intensity change frequency and the imaging cycle, and thus enable effective detection processing for flicker across a wide range of frequencies.

[0038] Figure 4 is a flowchart relating to the flicker detection process according to the first embodiment of the present invention. As shown in Figure 4, in step S401, the CPU 103 performs a photometric calculation of the subject to determine the exposure when the subject is imaged for the flicker detection process (subject photometric). Any method can be used for the photometric calculation. For example, in this embodiment, an evaluation value is obtained based on the average value of the image signal obtained by accumulating charge for photometric calculation using the image sensor 101. Then, the CPU 103 determines the representative luminance (photometric value) of the subject as a photometric result based on the obtained evaluation value. In this case, as a method for calculating the photometric value, the field of view corresponding to the image signal is divided into multiple blocks, the average value of the signal output from the corresponding pixel is obtained for each block, and the photometric value (representative luminance) is calculated by adding the average values ​​obtained for each block together. The unit of the photometric value is 1 BV in the so-called APEX (ADDITIVE SYSTEM OF PHOTOGRAPHIC EXPOSURE) system, which is one step of the luminance value, but other units can also be used.

[0039] Next, in step S402, the CPU 103 adjusts the imaging period to the imaging period (non-frame rate) for flicker detection. Details on how to adjust the imaging period for flicker detection will be described later.

[0040] Next, in step S403, the CPU 103 determines an exposure control value (changes the exposure) based on the previously obtained photometric value. The exposure control value in this embodiment is the shutter speed (i.e., storage time), aperture value, and shooting sensitivity (ISO sensitivity), which are parameters that can adjust the brightness of the image obtained by imaging the subject. The determined exposure control value is stored in the RAM mentioned above, and the exposure of the camera body 100 is changed, and the acquisition of an image for flicker detection begins.

[0041] Next, in step S404, the CPU 103 determines whether there is a change in brightness in the acquired image (i.e., whether or not flicker is occurring). As mentioned above, if the flashing cycle of the light source and the imaging cycle of the subject are synchronized, flicker cannot be detected correctly, so the presence or absence of a change in brightness is determined based on the acquired image. If it is determined that no change in brightness has occurred in the acquired image, the detection operation at the current frame rate (imaging cycle) is skipped, assuming that the imaging cycle and the frequency of the light intensity change of the flicker related to the subject are synchronized, or that no flicker is occurring.

[0042] If a change in brightness is detected in the acquired image (YES in step s404), the CPU 103 analyzes (detects) the presence or absence of flicker at multiple different frequencies in step S405. Details of the method for detecting flicker at multiple frequencies in step S405 will be described later.

[0043] Next, in step S406, the CPU 103 determines whether detection has been completed for a predetermined number (n) imaging cycles. If it is determined that detection has not been completed for the predetermined number of imaging cycles (NO in step S406), the process returns to step S402, the imaging cycle (frame rate) is changed, and the processing from S403 onwards is repeated.

[0044] If it is determined that detection has been completed for a predetermined number of imaging cycles (YES in step S406), in step S407 the CPU 103 identifies the flicker frequency of the subject based on the detection results up to step S405. In the processing of step S407, the presence or absence of flicker at multiple different frequencies at multiple imaging cycles (frame rates) has already been detected. Therefore, the flicker levels detected for each frequency are compared, and the flicker at the frequency with the highest level is identified as the flicker of the currently occurring subject, and this is the final detection result. In this embodiment, the magnitude of the light intensity change (the amplitude of the curve showing the regular change in light intensity) is compared as the flicker level, but this is not the only method. For example, a configuration that compares the degree of stability of the light intensity change, in addition to the flicker level, may also be adopted.

[0045] Here, we will specifically explain the imaging period (frame rate) for flicker detection mentioned above. As previously stated, the camera body 100 according to this embodiment performs flicker detection processing at multiple imaging periods. For example, consider the case where the imaging period is switched between 100fps and 120fps to detect the frequency of light intensity change of the flicker. In this case, for flicker whose light intensity changes at a period of k (k is a natural number) × 100Hz, such as 100Hz, 200Hz, 300Hz, which are integer multiples of the imaging period of 100fps, the imaging period and the frequency of light intensity change of the flicker are synchronized, and the flicker cannot be detected correctly. On the other hand, consider the case where the frequency of light intensity change of the flicker is detected at an imaging period of 120fps. In this case, for flicker whose light intensity changes at a period of m (m is a natural number) × 120Hz, such as 120Hz, 240Hz, 360Hz, which are integer multiples of the imaging period of 120fps, the imaging period and the frequency of light intensity change of the flicker are synchronized, and the flicker cannot be detected correctly. Note that 600Hz and 1200Hz, which satisfy both the conditions k × 100Hz (where k is a natural number) and m × 120Hz (where m is a natural number), are the least common multiples of 100Hz and 120Hz. When flicker occurs with light intensity changes at such frequencies, the frequency of the flicker's light intensity changes synchronizes with both imaging periods of 100fps and 120fps, making it impossible to correctly detect the flicker regardless of which imaging period is used to obtain the image.

[0046] For example, in light sources with rectifier circuits, such as LED light sources, the adjusted power supply frequency is generally within the range of 50Hz to 1000Hz. Therefore, even if the aforementioned 600Hz light intensity change frequency flicker occurs, it can still occur with LED light sources, but depending on the imaging period, the flicker may not be detected correctly. In other words, even if flicker detection is performed using images acquired with two different imaging periods, there are frequencies within the wide range of flicker frequencies that can occur with LED light sources that cannot be detected correctly.

[0047] In the example above, we described flicker that changes at a frequency that perfectly matches an integer multiple of the imaging period (frame rate). However, even if the frequency does not match an integer multiple of the imaging period, the accuracy of flicker detection may decrease. For example, for flicker that changes at a frequency close to an integer multiple of the imaging period used to acquire the image for flicker detection, the influence of exposure unevenness in the image is small, which may result in longer detection times or even failure to detect the flicker correctly.

[0048] Therefore, in this embodiment, in order to effectively detect flicker of a wide range of frequencies that may occur under an LED light source, the number n of multiple imaging periods (frame rates) used during flicker detection is adjusted to satisfy the condition that "n ≥ 3 (n is a natural number)". In other words, in this embodiment, flicker detection is performed with n or more imaging periods, which are natural numbers of 3 or greater.

[0049] Furthermore, as the frequency of the light intensity change of the flicker to be detected increases, increasing the number of imaging cycles n used for detection allows for more accurate detection of the flicker's light intensity change frequency. However, increasing the number of imaging cycles used for flicker detection may extend the period involved in flicker detection, and it is necessary to consider the resulting decrease in release time lag and the display frame rate of the live view image. Therefore, in this embodiment, the number of imaging cycles used for flicker detection is set to n=3, which is the sampling number that can effectively detect flicker that may occur in light sources that are commonly used, such as LED light sources.

[0050] Next, we will explain how to select specific numerical values ​​for each of the n imaging periods. In this embodiment, a reference imaging period is first set. For example, let's assume a reference imaging period of 100 fps. The frequency of light intensity change of flicker synchronized with an imaging period of 100 fps is an integer multiple of 100 Hz, and if flicker of this light intensity change frequency occurs, the flicker cannot be detected correctly.

[0051] Furthermore, the same problems occur when sampling at an imaging period of 200fps, which is twice the reference imaging period of 100fps. In other words, if an integer multiple of the imaging period required to obtain the image for flicker detection coincides with an integer multiple of the frequency of the flicker's light intensity change, the imaging period and the light intensity change frequency become synchronized, making it impossible to correctly detect flicker based on the image acquired for sampling.

[0052] Therefore, in this embodiment, as n imaging periods (n=3 in this embodiment), the remaining n-1 (2 in this embodiment) imaging periods are set between the reference imaging period and the next imaging period that is an integer multiple of the reference imaging period. For example, when detecting flicker with 3 imaging periods and a reference imaging period of 100fps, the remaining imaging periods for detecting flicker are set between 100fps and 200fps, in addition to 100fps. In this embodiment, each imaging period (frequency) is set such that the least common multiple of the n imaging periods is greater than or equal to a predetermined frequency. For example, since the flickering frequency of an LED light source is generally 10000Hz or less, the frequency of each imaging period is determined as a predetermined frequency such that the least common multiple of the n imaging periods (frame rates) is 10000 or more. Furthermore, in order to reduce the effects of flicker in the camera body 100, each imaging period (frequency) is set such that the least common multiple of n imaging periods is greater than the reciprocal of the upper limit of the high-speed shutter speed that the camera body 100 can set. With this configuration, it is possible to effectively detect flicker generated by light sources that change in light intensity at high frequencies, such as LED light sources, and to reduce the effects of the detected flicker by adjusting the shutter speed.

[0053] Figure 5 is a diagram illustrating an illustrative method for selecting multiple imaging periods when detecting flicker according to the first embodiment of the present invention. In order to accurately detect the light intensity change frequency of the flicker, by spacing out the imaging periods as much as possible, it is possible to ensure a difference between any of the multiple imaging periods and the light intensity change frequency of the flicker to be detected (the blinking period of the light source) to a degree that allows for good detection of the flicker. Therefore, in this embodiment, as shown in Figure 5(a), in order to divide the range of imaging periods to be detected (100fps to 200fps) into predetermined intervals, imaging periods are set that are separated by 1 / 3 of each imaging period 2 to detect the flicker.

[0054] Specifically, in this embodiment, as shown in Figure 5(a), the three imaging periods are set to a reference imaging period of 100 fps, 100 fps × 2^(1 / 3) = 125.99 fps ≈ 126 fps, and 100 fps × 2^(2 / 3) = 158.74 fps ≈ 159 fps. Since these three imaging periods differ by 2^(1 / 3) = 1.2599 ≈ 1.26 times each, each imaging period differs by approximately 26%. With this configuration, even when flicker detection is performed by dividing a wide frequency range of 50 to over 1000 Hz into multiple ranges, the frequency of each range does not deviate significantly from the frequency to be detected. Furthermore, at least one of the imaging periods can be sufficiently differentiated from the frequency of light intensity change of the flicker to be detected. In other words, when setting n imaging periods and detecting flicker at each imaging period, the decrease in detection accuracy for each frequency of the target can be suppressed by setting each imaging period at intervals of 2 to the power of (1 / n).

[0055] Figure 5(b) is a diagram illustrating the correspondence between n imaging periods and the light intensity change frequencies of the flicker to be detected. In this embodiment, flicker is detected based on the image obtained from the imaging period that has the frequency furthest from the light intensity change frequency of the flicker to be detected among the n imaging periods. Specifically, in this embodiment, as shown in Figure 5(b), flicker detection is performed based on a data table that divides the light intensity change frequencies of flicker from 50 Hz to 1008 Hz into ranges (A) to (P) for the three imaging periods shown in Figure 5(a).

[0056] In this embodiment, the subject is imaged at a shutter speed that is the reciprocal of the flicker's light intensity change frequency, thereby setting an imaging period synchronized with the flicker's light intensity change frequency and reducing the effect of flicker. Therefore, if there is a discrepancy between the ideal shutter speed synchronized with the flicker's light intensity change frequency and the actual shutter speed, the effect of flicker on the image (such as uneven exposure) is greater at slower shutter speeds than at faster shutter speeds. For example, consider the case where shutter speeds of 1 / 101 second and 1 / 1001 second are set for flicker with light intensity change frequencies of 100 Hz and 1000 Hz, respectively, resulting in a 1 Hz discrepancy from the ideal shutter speed for reducing the effect of flicker. In both cases, there is a 1 Hz discrepancy between the shutter speed that can reduce the effect of flicker and the actual shutter speed, but the discrepancy is 1% at a shutter speed of 1 / 100 second, while it is 0.1% at a shutter speed of 1 / 1000 second. In other words, the effect of flicker on the image is smaller for a 1 Hz change in shutter speed at faster shutter speeds. However, when the shutter speed is long, the period for capturing light intensity changes caused by flicker becomes longer, increasing the likelihood of obtaining an image with smoothed light intensity changes. Therefore, when detecting flicker with light intensity change frequencies that are reduced by shutter speeds above a predetermined value (for example, long exposures of 1 / 25 second or longer), the detection range in the low-frequency region of the flicker may be appropriately adjusted and widened.

[0057] Therefore, in this embodiment, as shown in Figure 5(b), the range of the light intensity change frequency of the flicker to be detected is divided into multiple ranges, and the detection range is set such that the frequency of each of these consecutive ranges differs by 2^(1 / 3) = 1.26 times. For example, while the range (N) shown in Figure 5(b) is 159~200Hz, the next range (C) is a detection range for flicker in the 200~252Hz range, which is approximately 1.26 times that of range (N).

[0058] As shown in Figure 5(b), the range of flicker light intensity change frequencies that can be detected for the same imaging period differs by approximately a factor of two within a continuous range. For example, the detection target frequencies for ranges (A), (B), and (c) shown in Figure 5(b), where 159 fps corresponds to the imaging period, ranges from 50 Hz, 100 Hz, and 200 Hz to 63 Hz, 126 Hz, and 252 Hz, respectively. This is because the change in light intensity due to flicker is the same at integer multiples of each frequency, and with the above configuration, the imaging device according to this embodiment can detect a wide range of frequency flicker with stable accuracy.

[0059] In this embodiment, the imaging period for detecting flicker is configured such that each imaging period differs by a factor of m^(1 / n) (where m and n are natural numbers). Although m=2 was used in the above explanation, it is not limited to this value. For example, the imaging period may be set to m=3. In this case, the difference between imaging periods will be larger, and the detection accuracy for the light intensity change frequency of the flicker being detected may be lower than when m=2. However, when detecting within the same frequency range, m=3 can shorten the detection time compared to m=2, making it suitable for detecting a wider range of flicker light intensity change frequencies.

[0060] Here, a method for selecting n imaging periods, different from the method described above (a modified version), will be explained with reference to Figure 6. Figure 6 is a diagram illustrating a modified version of the method for selecting multiple imaging periods when detecting flicker according to the first embodiment of the present invention. The difference between this modified version and the example described above with reference to Figure 5 is the method for setting n imaging periods with respect to the range of imaging periods to be detected.

[0061] In this modified example, as shown in Figure 6(a), multiple imaging periods are set by equally dividing the range of imaging periods to be detected. That is, if the range of imaging periods for flicker detection (100fps to 200fps) is set as 100%, then n imaging periods are set to differ by 33% and 66% respectively from the reference imaging period of 100fps. Specifically, the three imaging periods are set to a reference imaging period of 100fps, 100fps × 1.333 = 133.333...fps ≈ 133fps, and 100fps × 1.666 = 166.666fps ≈ 167fps.

[0062] Furthermore, the differences in the three imaging periods mentioned above are 133.333 / 100 = 1.33333, 166.666 / 133.33 = 1.25, and 200 / 166.666 = 1.2, indicating that each imaging period is more than 20% apart.

[0063] Figure 6(b) is a diagram illustrating the correspondence between the light intensity change frequencies of the flicker to be detected and the n imaging periods shown in Figure 6(a). As shown in Figure 6(b), in this modified example, as in Figure 5(b) described above, the flicker is detected based on the image obtained using the imaging period that has the frequency furthest from the light intensity change frequency of the flicker to be detected among the n imaging periods.

[0064] Here, we will explain the differences between multiple imaging periods used for flicker detection. As mentioned above, when considering the number of imaging periods used for flicker detection, the difference between each imaging period decreases as the number increases, but the time required for sampling increases. Therefore, in order to accurately detect flicker in a short period of time, it is preferable to have as large a difference between each imaging period as possible, while keeping the number of imaging periods used for sampling to a minimum, within a range where a wide range of flicker light intensity change frequencies can be detected.

[0065] As explained with reference to Figure 5, we will describe the case where the period from the reference imaging period to twice the reference imaging period is defined as 100%, and this period is divided into 2 to the power of 1 / n. In this case, multiple imaging periods for flicker detection differ at intervals shown in the following equation (1). {2^(1 / n)-1}×100[%] (Formula 1)

[0066] Furthermore, we consider the case where the period from the reference imaging period to twice the reference imaging period is defined as 100%, and the period within that range differs by 100 / n[%], as explained with reference to Figure 6. As calculated for n=3, the smallest difference is observed between an imaging period 100% × (n-1) / n away from the reference imaging period and an imaging period twice the reference imaging period. This difference is [200 / {100+{(100×(n-1) / n}-1] × 100[%] ={200n / (200n-100)-1} [%] ={2n / (2n-1)-1}×100[%] ={1 / (2n-1)}×100[%] (Formula 2) This is how it is determined. That is, when each imaging period differs by 100 / n[%], the multiple imaging periods (frame rates) used for flicker detection differ from each other by at least a ratio of [{2n / (2n-1)-1}] × 100% or more. In addition, in the camera body 100 according to the first embodiment of the present invention, the multiple imaging periods (frame rates) used for flicker detection differ from each other by at least a difference of [{2n / (2n-1)}-1] × 100% or more. This also includes the case described above where the period from the reference imaging period to twice the reference imaging period is taken as 100%, and that period is divided into 2 to the power of 1 / n.

[0067] Here, based on equations 1 and 2 described above, the relationship between the method for determining each imaging period and the difference in the number of imaging periods is shown in Figure 7. Figure 7 is a diagram (graph) illustrating the relationship between the method for determining each imaging period for flicker detection and the number of imaging periods according to this embodiment. As shown in Figure 7, the difference for each imaging period corresponding to the difference in the number of imaging periods n is smaller for equation 2, which is shown as a solid line in the figure, than for equation 1, which is shown as a dashed line. This condition is also true when considering an even larger number of imaging periods n, which is not shown in Figure 7. In other words, although two different methods for determining imaging periods were described in the example above, it can be seen that in both methods, the difference for each imaging period is greater than the value obtained by equation 2.

[0068] Next, we will explain in detail the process of analyzing (detecting) the presence or absence of flicker at multiple different frequencies in step S405 described above. In the imaging device according to this embodiment, changes in brightness over time are extracted based on the brightness of the continuously acquired images, and the frequency of the light intensity change of the flicker is detected by analyzing the periodicity of the brightness change. Note that the brightness changes that occur in the image differ depending on the image acquisition method used for detection. For example, the brightness changes in the image differ when imaging a subject with a so-called global shutter method such as a CCD compared to when imaging a subject with a so-called rolling shutter method such as a CMOS. The following will explain how brightness changes when acquiring images with each of the above methods.

[0069] First, let's explain the brightness change in an image obtained using the global shutter method, referring to Figure 8. Figure 8 is a diagram illustrating the brightness change based on images continuously obtained using the global shutter method. When a subject is imaged that is affected by the flickering of a light source due to flicker, the resulting image is affected by the intensity of the light source's flickering. When the brightness of the entire image is measured, the resulting photometric value is affected by the intensity of the light source's flickering.

[0070] In this explanation, luminance may refer to the luminance signal calculated by multiplying the R·G1·G2·B signals in a RAW image of a Bayer array by a certain coefficient, or it may refer to the color signals of the R·G1·G2·B signals themselves. It may also refer to color signals and luminance signals obtained from sensor arrays other than Bayer arrays.

[0071] Then, using the captured images obtained by the method described above, the difference or ratio of the brightness (photometric values) of multiple consecutive images is calculated. Alternatively, the difference / ratio of the brightness of each image relative to the reference image is calculated using an average image of multiple images. By plotting the brightness changes for each image obtained in this way, it is possible to detect the changes in the brightness of the images as shown in Figure 8.

[0072] Next, with reference to Figure 9, we will explain the brightness changes in images obtained using the rolling shutter method. Figure 9 is a diagram illustrating the brightness changes based on images continuously obtained using the rolling shutter method. When driving the sensor with the rolling shutter method, the exposure and readout timing differs for each row (line) of the sensor. Therefore, the effect of the flickering of the light source caused by flicker differs for each row (line), resulting in different brightness changes in the vertical direction of the image.

[0073] Therefore, when driving the sensor (image sensor 101 in this embodiment) using a rolling shutter method, changes in brightness due to the flickering of a light source can be extracted by acquiring an integral value for each row (line) of the captured image. Specifically, as shown in Figure 9, the brightness change of the same line in the N-1th and Nth consecutive frames of an image obtained by continuously capturing a subject is extracted. In this case, an integral value is calculated for each row of the captured image corresponding to the Nth and N-1th frames. As mentioned above regarding the global shutter method, this integral value may be a brightness signal obtained by multiplying the color signal by a certain ratio, or it may be the integral of the color signal itself. By comparing these integral values ​​of the Nth and N-1st frames row by row and calculating the difference / ratio, it is possible to detect changes in brightness in the vertical direction of the captured image (i.e., the scanning direction of the sensor), as shown in Figure 9.

[0074] Note that the frames used for comparison do not necessarily have to be two consecutive frames. For example, the signal values ​​of multiple captured images can be averaged to obtain an average image, and this average image can be used as a reference image. The integral value for each line can then be compared with the integral value for each line in the Nth frame to calculate the vertical brightness change of the image.

[0075] By analyzing the images captured using the rolling shutter method as described above, it is possible to detect the changes in vertical brightness in the captured images, and these brightness changes represent the flickering of the light source (i.e., changes in the amount of flicker light).

[0076] Next, we will explain a method for analyzing the frequency of brightness changes from the progression of brightness changes in an image. A common method for converting a time-varying signal into frequency components is the Fourier transform. In this case, a time-varying signal f(t) is converted into a frequency function F(ω).

[0077]

number

[0078] In equation 3, focusing on the exponential function, it is generally known that the exponential function can be expanded into real and imaginary trigonometric functions due to the relationship between the Maclaurin series and the nth derivative of trigonometric functions (as shown in equation 4 below).

[0079]

number

[0080] Furthermore, by letting f(t) be the progression of the image signal and dt be the sampling interval for the progression of the signal, the integral can be calculated, and therefore Equation 4 can be expressed as Equation 5 below. F(ω) = A(ω) + j × B(ω) (Equation 5) Since this is a complex function with respect to frequency ω, its magnitude is calculated as |F(ω)|. If the luminance change component due to frequency ω is included in the transition of the image's luminance change, |F(ω)| will be a large value, and if the luminance change component due to frequency ω is not included in the transition of the image's luminance change, |F(ω)| will be a small value. In other words, |F(ω)| can be considered as the flicker level for each frequency. Therefore, by calculating each frequency component using equation 5 described above for a wide range of frequencies to be detected, it is possible to detect the presence or absence of luminance changes due to the flickering of a light source (i.e., the frequency of light intensity changes of flicker) over a wide frequency range.

[0081] Furthermore, if the change in brightness does not include more than one cycle of the light source's flickering (one cycle of the flicker's light intensity change), the target frequency may not be detected properly and may be mistakenly detected as another frequency. Therefore, it is preferable to continue imaging the subject for more than one cycle period of the frequency to be detected and to detect each of the above frequencies (i.e., the flicker's light intensity change frequency) based on the image obtained from the imaging.

[0082] Next, we will specifically explain the exposure operation during flicker detection in step S403 mentioned above. As previously stated, if the imaging period when detecting flicker and the frequency of the light source's flickering (the frequency of the flicker's light intensity change) are synchronized, it is difficult to effectively detect flicker based on the sampled image. Furthermore, even if the exposure time (i.e., shutter speed) when imaging the subject is synchronized with the light source's flickering frequency, the image obtained in this state will not show an effective change in brightness, making it difficult to detect flicker.

[0083] Therefore, in this embodiment, when performing the flicker detection operation, the exposure time (shutter speed) is set to be synchronized with each imaging period so as not to be synchronized with frequencies other than each imaging period. In other words, when detecting flicker, it is preferable to image the subject with an exposure time (shutter speed) that is 1 / N (where N is an integer) of the detection imaging period (frame rate).

[0084] Figure 10 is a diagram illustrating, in part, the exposure time (shutter speed) settings in a first pattern of multiple imaging cycles for flicker detection according to the first embodiment of the present invention. For example, as mentioned above, if the multiple imaging cycles for flicker detection are 100fps, 126fps, and 159fps, the subject is imaged with the exposure time shown in Figure 10.

[0085] Figure 11 is a diagram illustrating, in part, the exposure time (shutter speed) settings in a second pattern of multiple imaging cycles for flicker detection according to the first embodiment of the present invention. For example, as mentioned above, if the multiple imaging cycles for flicker detection are 100fps, 133fps, and 167fps, the subject is imaged with the exposure time shown in Figure 11.

[0086] As illustrated in Figures 10 and 11, by acquiring an image for flicker detection with an exposure time that is 1 / N (where N is an integer) of the imaging period (frame rate) for flicker detection, it is possible to prevent synchronization between the exposure time and the frequency of light intensity changes of the flicker.

[0087] Furthermore, if the exposure conditions differ at each frequency of the flicker light intensity change, differences will occur in the detected flicker level, reducing the accuracy of detection. Therefore, in this embodiment, by performing the exposure operation in the multiple imaging cycles described above based on the photometric result in step S401, differences in exposure amount for each imaging cycle are suppressed, enabling stable detection of the flicker level.

[0088] By adopting the configuration described above, the imaging device according to this embodiment can stably and effectively detect flicker across a wide range of frequencies that can be considered as the frequency of light intensity changes for flicker.

[0089] Next, with reference to Figure 12, the details of the flicker reduction exposure time determination process performed in step S304 described above will be explained. Figure 12 is a flowchart relating to the flicker reduction exposure time determination process according to the first embodiment of the present invention. First, in step S1201, the CPU 103 reads the flicker light intensity change frequency detected by the flicker detection process performed in step S302 described above from memory.

[0090] Next, in step S1202, the CPU 103 calculates the ideal exposure time (IdealFlkExpTime) to reduce the effect of the detected flicker, based on the reciprocal of the flicker light intensity change frequency read in step S1201. For example, if the detected flicker light intensity change frequency is 540.0 Hz, then IdealFlkExpTime = 1 / 540.0.

[0091] Next, in step S1203, the CPU 103 obtains the currently set shutter speed (CurTv). The current shutter speed CurTv may be, for example, the shutter speed set manually by the user. In this embodiment, it is assumed that the shooting mode of the camera body 100 is set to manual mode in advance, and that all of the multiple exposure control values ​​(parameters) are set manually by the user.

[0092] Next, in step S1204, the CPU 103 performs an initialization process to integer-multiply the ideal flicker reduction exposure time, IdealFlkExpTime. Specifically, in step S1204, the integer N is set to 1, and the information of the ideal flicker reduction exposure time, IdealFlkExpTime, before integer multiplication is stored as PreIdealFlkExpTime.

[0093] Next, in step S1205, the CPU 103 compares the currently set shutter speed CurTv, obtained in step S1203, with the ideal flicker reduction exposure time IdealFlkExpTime. If the value of CurTv is less than or equal to IdealFlkExpTime (i.e., the exposure time is short), the process proceeds to step S1207 (determined as YES in step S1205). On the other hand, if CurTv is greater than IdealFlkExpTime (i.e., the exposure time is long), the process proceeds to step S1206 (determined as NO in step S1205).

[0094] In step S1206, the CPU 103 stores the current ideal flicker reduction exposure time as the previous PreIdealFlkExpTime, increments the integer N by one, and then multiplies the ideal flicker reduction exposure time by an integer N. Specifically, in step S1206, IdealFlkExpTime is substituted for PreIdealFlkExpTime, N is incremented to N=N+1, and then IdealFlkExpTime is multiplied by an integer N. The process in step S1206 is repeated until the shutter speed currently set in step S1205 is less than or equal to the ideal flicker reduction exposure time (CurTv ≤ IdealFlkExpTime). In other words, the process in step S1206 is to bring the ideal flicker reduction exposure time, IdealFlkExpTime, as close as possible to the currently set shutter speed. As a result of this process, CurTv is located between IdealFlkExpTime and PreIdealFlkExpTime, so for example, the flicker reduction exposure time can be narrowed down to an exposure time close to the shutter speed set by the user.

[0095] Next, in step S1207, the CPU 103 compares the absolute difference between the values ​​of IdealFlkExpTime and PreIdealFlkExpTime and CurTv. If the result in step S1207 is NO, the current flicker reduction exposure time determination process is terminated. This is because the currently set ideal flicker reduction exposure time, IdealFlkExpTime, is determined to be closer to the current shutter speed than PreIdealFlkExpTime.

[0096] Conversely, if the result in step S1207 is YES, it can be determined that the previously set ideal flicker reduction exposure time, PreIdealFlkExpTime, is closer to the current shutter speed than the currently set ideal flicker reduction exposure time. Therefore, in this case, the process proceeds to step S1208, where the CPU 103 replaces the previously set PreIdealFlkExpTime with the ideal flicker reduction exposure time, IdealFlkExpTime, and terminates the process of determining the current flicker reduction exposure time.

[0097] According to the flicker reduction exposure time determination process of this embodiment described above, for example, the exposure time (shutter speed) for reducing flicker can be determined at a value close to the shutter speed set by the user. With this configuration, for example, it is possible to obtain an image with reduced flicker effects while suppressing differences in the intended shooting effect caused by the user adjusting the shutter speed.

[0098] Figure 13 illustrates an example of how to set the ideal flicker reduction exposure time when flicker occurs that changes at a predetermined light intensity change frequency according to the present invention. Figure 13(a) shows, for example, a case where the shutter speed is set to 1 / 5792.6 by the user (CurTv=1 / 5792.6). Figure 13(b) shows, for example, a case where the shutter speed is set to 1 / 250.5 by the user (CurTv=1 / 250.5).

[0099] For example, if the detected flicker light intensity change frequency is 540.0 Hz, the ideal flicker reduction exposure time (IdealFlkExpTime) in the example shown in Figure 13(a) is 1 / 540.0. Also, for the same flicker light intensity change frequency, the ideal flicker reduction exposure time (IdealFlkExpTime) in the example shown in Figure 13(b) is 1 / 270.0. The flicker light intensity change is the same at integer multiples of the frequency. Therefore, even when imaging a subject at a shutter speed that is slower than the reciprocal of the flicker light intensity change frequency, and where the shutter speed is the reciprocal of an integer multiple of the flicker frequency, the effect of flicker can be reduced. Thus, if the shutter speed set by the user is less than or equal to the reciprocal of the detected flicker light intensity change frequency, the ideal flicker reduction exposure time should be the value among the reciprocals of integer multiples of the flicker frequency that has a small difference from the shutter speed set by the user.

[0100] Next, with reference to Figure 14, the details of the shutter speed selection process performed in step S305 described above will be explained. Figure 14 is a flowchart relating to the shutter speed selection process according to the first embodiment of the present invention. First, in step S1401, the CPU 103 performs an initialization process to select an arbitrary shutter speed from the shutter speed setting (index) table described above with reference to Figure 2. Specifically, in step S1401, the CPU 103 sets the configurable flicker reduction shutter speed (SetPosFlkTv) from the shutter speed setting table with index i=1. In this embodiment, as shown in Figure 2, when index i=1, SetPosFlkTv=1 / 8192.0.

[0101] Next, in step S1402, the CPU 103 increments index i in the shutter speed setting table by one. Then, in step S1403, the CPU 103 compares the absolute difference between SetPosFlkTv and shutter speed[i] in the shutter speed setting table with the aforementioned ideal flicker reduction exposure time, IdealFlkExpTime. If the difference between SetPosFlkTv and IdealFlkExpTime is less than or equal to the difference between shutter speed[i] and IdealFlkExpTime (determined as NO in step S1403), the process proceeds to step S1405.

[0102] On the other hand, if it is determined that the difference between SetPosFlkTv and IdealFlkExpTime is greater than the difference between shutter speed[i] and IdealFlkExpTime (determined as YES in step S1403), the process proceeds to step S1404. Then, in step S1404, the CPU 103 selects a configurable flicker reduction shutter speed based on the determination result in step S1403. Specifically, in step S1404, the CPU 103 sets the configurable flicker reduction shutter speed SetPosFlkTv to the shutter speed[i] corresponding to index i in the current shutter speed setting table, and proceeds to step S1405.

[0103] Next, in step S1405, the CPU 103 determines whether index i in the shutter speed setting table is greater than or equal to the maximum index. If the current index [i] is less than the maximum index (determined as NO in step S1405), the process returns to step S1402 and steps S1402 to S1405 are repeated. In this embodiment, the maximum index is 600, as shown in Figure 2. If it is determined in step 1405 that the current index [i] has reached the maximum index (step S1405 is YES), the current SetPosFlkTv is selected as the configurable flicker reduction shutter speed, and the shutter speed selection process ends.

[0104] In the example described above, the shutter speed selection process was performed on all indices accessible in the shutter speed setting table, but it is not limited to this. For example, in the flicker reduction exposure time determination process, if the currently set shutter speed CurTv is obtained, the settable flicker reduction shutter speeds may be determined by narrowing the scope to the vicinity of that CurTv. Specifically, if a particular value is recorded as the currently set shutter speed CurTv, the index corresponding to the shutter speed closest to CurTv is identified. Then, the difference between that index and the ideal flicker reduction exposure time is calculated for the shutter speeds corresponding to that index and other indices adjacent to it, and the shutter speed with the smallest difference is set as the settable flicker reduction shutter speed. This configuration is particularly effective when a specific shutter speed is set by the user. By adopting this configuration, the discrepancy with the shutter speed intended by the user is reduced, and the processing time and processing load related to the shutter speed selection process can be reduced by significantly reducing the number of indices used for comparison.

[0105] By performing the shutter speed selection process described above, the camera body 100 can select a shutter speed from among the settable shutter speeds that can effectively reduce the effects of pre-detected flicker. In other words, the camera body 100 of this embodiment can select (set) the shutter speed that is closest to the ideal shutter speed, IdealFlkExpTime, for reducing the effects of detected flicker, from among the settable shutter speeds.

[0106] Figure 15 is a diagram illustrating the relative relationship between the shutter speed selected by the shutter speed selection process according to the first embodiment of the present invention and the ideal shutter speed for reducing the effect of flicker. In Figure 15, it is assumed that the flicker light intensity change frequency is 540.0 Hz and the ideal flicker reduction exposure time, IdealFlkExpTime, is 1 / 540.0. Figure 15(a) shows the case where the shutter speed (CurTv) currently set by the user is 1 / 5792.6, and Figure 15(b) shows the case where the shutter speed (CurTv) currently set by the user is 1 / 250.5.

[0107] Here, in Figure 15(a), the difference between Tv=1 / 546.4, indicated by index 58 in the shutter speed setting table, and IdealFlkExpTime, Tv=1 / 540.0, is shown as Δ58. Also, in Figure 15(a), the difference between Tv=1 / 534.7, indicated by index 59 in the shutter speed setting table, and IdealFlkExpTime, Tv=1 / 540.0, is shown as Δ59. In the case shown in Figure 15(a), Δ59 < Δ58, so Tv=1 / 534.7 is selected as SetPosFlkTv by the shutter speed selection process described above.

[0108] Furthermore, in Figure 15(b), the difference between Tv=1 / 273.2, indicated by index 119 in the shutter speed setting table, and IdealFlkExpTime, Tv=1 / 270.0, is shown as Δ119. Also, in Figure 15(b), the difference between Tv=1 / 270.2, indicated by index 120 in the shutter speed setting table, and IdealFlkExpTime, Tv=1 / 270.0, is shown as Δ120. In the case shown in Figure 15(b), Δ120 < Δ119, so Tv=1 / 270.2 is selected as SetPosFlkTv by the shutter speed selection process described above.

[0109] As described above, the camera body 100 of this embodiment can effectively detect the frequency of light intensity changes of flicker occurring in the current shooting environment, and the ideal shutter speed (exposure time) that reduces the effects of the detected flicker, in the shortest possible time.

[0110] Furthermore, the camera body 100 of this embodiment can set a shutter speed that takes into account the currently set shutter speed by the user or the like as the ideal shutter speed for reducing the effects of flicker. Therefore, the camera body 100 of this embodiment can detect a shutter speed that can reduce the effects of flicker while minimizing any difference from the exposure conditions and shooting effects intended by the user.

[0111] Furthermore, the camera body 100 of this embodiment can automatically select (set) the shutter speed that is closest to the ideal shutter speed that can reduce the effects of flicker, among the shutter speeds that the camera body 100 can set. Therefore, the camera body 100 of this embodiment can automatically select (set) a shutter speed that can reduce the effects of flicker without requiring manual adjustment of the shutter speed by the user.

[0112] Next, with reference to Figures 16 and 17, the details of the display processing in step S306 described above according to the first embodiment of the present invention will be explained. Figure 16 is a diagram illustrating an example of a notification image displayed on the display unit 102 by the display processing according to the first embodiment of the present invention. Of these, Figure 16(a) shows the case where a 540.0 Hz flicker is detected, with CurTv being 1 / 5792.6 and SetPosFlkTv being 1 / 534.7. Figure 16(b) shows the case where a 540.0 Hz flicker is detected, with CurTv being 1 / 250.5 and SetPosFlkTv being 1 / 270.2. Figure 17 is a diagram illustrating an example of a notification image when no flicker is detected by the display processing according to the first embodiment of the invention.

[0113] The detected flicker region 1601 displays information indicating the frequency of the light intensity change of the flicker detected based on the method described above (540.0 Hz in the illustrated example).

[0114] The selectable shutter speed area 1602 displays the configurable flicker reduction shutter speed SetPosFlkTv, which is determined based on the method described above (Figure 16(a) shows the case of 1 / 534.7, and Figure 16(b) shows the case of 1 / 250.5).

[0115] Currently, the shutter speed range 1603 displays the shutter speed currently set on the camera body 100, as determined by the user's manual settings (Figure 16(a) shows 1 / 5792.6, and Figure 16(b) shows 1 / 270.2).

[0116] The first user selection icon 1604 displays an option for users who do not agree to the change to the configurable flicker reduction shutter speed SetPosFlkTv shown on the notification screen. The second user selection icon 1605 displays an option for users who agree to the change to the configurable flicker reduction shutter speed SetPosFlkTv shown on the notification screen.

[0117] Furthermore, if the flicker detection process does not detect flicker above a predetermined level, a descriptive message 1701 indicating that no flicker was detected, and an icon 1702 allowing the user to input whether or not they want to confirm, will be displayed on the display unit 102, as shown in Figure 17.

[0118] As described above, when flicker of a predetermined light intensity change frequency is detected by the flicker detection process, various icons and text as shown in Figures 16(a) and (b) are displayed on the display unit 102, prompting the user to change the shutter speed. This configuration allows for easy setting of a shutter speed that can reduce the effects of flicker, while reducing the need for manual adjustment by the user to adjust the shutter speed to reduce the effects of flicker. Therefore, the camera body 100 according to the present invention can perform imaging with reduced flicker effects across a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operations, and can reduce unevenness in images caused by flicker.

[0119] The methods for informing the user about the frequency of flicker light intensity changes and shutter speeds that can reduce the effects of flicker, as well as how to change the shutter speed, are not limited to those described above. For example, although the above example described the case where a notification image is displayed on the display unit 102, the notification image may also be displayed on other display devices or on external devices connected to the camera body 100. Furthermore, the method of notification is not limited to image display. Various notification means can be used as substitutes, such as voice guidance or changes in the illumination status or color of a lamp (not shown) provided on the camera body 100.

[0120] Furthermore, while the camera body 100 in this embodiment employs a method to confirm with the user whether or not to change to a configurable flicker-reducing shutter speed, it is not limited to this. For example, it may be configured to automatically change to a configurable flicker-reducing shutter speed without the user's consent, or it may be configured to determine whether or not to confirm with the user whether or not to change to a configurable flicker-reducing shutter speed depending on the shooting mode. In this case, if the shooting mode is an auto mode in which the camera body 100 automatically determines each parameter related to exposure control, it is preferable for the camera body 100 to automatically set the flicker reduction shutter speed. On the other hand, if the shooting mode is a manual mode in which the user manually sets each parameter related to exposure control (exposure control value), it is preferable to adopt a method of confirming with the user whether or not to change the shutter speed, as in the example above.

[0121] Furthermore, while the camera body 100 according to this embodiment prioritizes the use of an electronic shutter as described above, it is not limited to this. For example, a configuration in which a mechanical shutter 104 is used to adjust the exposure time of the image sensor 101 according to an arbitrary shutter speed is also possible.

[0122] Furthermore, when using the mechanical shutter 104 to set a high shutter speed and image a subject, the timing of the mechanical shutter 104's movement relative to the ideal exposure time may be off due to changes in the physical characteristics of the mechanical shutter 104 or differences in the environment. In other words, if the shutter speed set as the configurable flicker reduction shutter speed SetPosFlkTv is high, it may not be possible to image the subject with an exposure time that can properly reduce the flicker effect.

[0123] Therefore, when adjusting the exposure time using the mechanical shutter 104, the configurable flicker reduction shutter speed SetPosFlkTv may be limited so that the shutter speed is greater than or equal to a predetermined speed. The predetermined speed (shutter speed) should be a value such that the difference (i.e., error) between the ideal exposure time and the timing of exposure and shading of the image sensor 101 by the driving of the mechanical shutter 104 falls within a predetermined range. In this embodiment, as an example, the predetermined shutter speed is set to 1 / 4000 second. In this case, the aforementioned shutter speed setting table can be used within the range excluding the index corresponding to shutter speeds of 1 / 4000 second or less, or the configurable flicker reduction shutter speed can be determined using new table data.

[0124] Furthermore, the camera body 100 in this embodiment may be configured to dynamically adjust whether to use an electronic shutter or a mechanical shutter 104 depending on the value of the configurable flicker reduction shutter speed SetPosFlkTv. For example, only the electronic shutter may be available when the shutter speed is faster than 1 / 4000 second, while both the electronic shutter and the mechanical shutter 104 may be available at other shutter speeds.

[0125] (Second Embodiment) In the first embodiment described above, a configuration was described in which only one configurable flicker reduction shutter speed was notified to the user. In contrast, in this embodiment, a configuration in which multiple options for configurable flicker reduction shutter speeds are notified to the user will be described with reference to Figure 18. Note that the configuration and basic driving method of the camera body 100, lens unit 200, and light-emitting device 300, which are imaging devices according to this embodiment, are substantially the same as those of the first embodiment described above, so the reference numerals for each part are the same and the description is omitted. The difference between this embodiment and the first embodiment described above is the display processing in step S306.

[0126] Figure 18 is a diagram illustrating an example of a notification image displayed on the display unit 102 by the display processing according to the second embodiment of the present invention. Of these, Figure 18(a) shows the case where a 540.0 Hz flicker is detected, and the CurTv is 1 / 5792.6 and the SetPosFlkTv is 1 / 534.7. Also, Figure 18(b) shows the case where a 540.0 Hz flicker is detected, and the CurTv is 1 / 250.5 and the SetPosFlkTv is 1 / 270.2.

[0127] The detected flicker area 1801 displays information indicating the frequency of light intensity changes of detected flickers. The current shutter speed area 1802 displays the shutter speed currently set on the camera body 100, such as through the user's manual settings (Figure 18(a) shows 1 / 5792.6, and Figure 18(b) shows 1 / 270.2).

[0128] In the first candidate area 1803 for selectable shutter speeds, the configurable flicker reduction shutter speed SetPosFlkTv, determined based on the method described in the first embodiment, is displayed as the first candidate shutter speed selectable by the user. Note that Figure 18(a) shows the first candidate area 1803 for 1 / 534.7, and Figure 18(b) shows it for 1 / 270.2.

[0129] In the second candidate range of selectable shutter speeds 1804, the shutter speeds corresponding to the index with the next smallest difference from IdealFlkExpTime after SetPosFlkTv are displayed as the second candidate shutter speeds that the user can select. In Figure 18(a), the second candidate range of selectable shutter speeds 1804 is shown as 1 / 546.4, and in Figure 18(b), it is shown as 1 / 273.2.

[0130] In the selectable shutter speed candidate area 1805, if there is a shutter speed that is more effective in reducing the effect of flicker, regardless of the difference with CurTv, that shutter speed will be displayed as an alternative shutter speed that the user can select. For example, Figure 18(a) shows an example where 1 / 270.2, which is close to Tv=1 / 270.0 (twice IdealFlkExpTime Tv=1 / 540.0), is displayed in the selectable shutter speed candidate area 1805. If 540Hz flicker is detected, Tv=1 / 270.2 has a larger difference from the difference with CurTv, but it is more effective in reducing the effect of flicker than SetPosFlkTv(1 / 534.7).

[0131] The shutter speed selection icon 1806 displays icons for the user to select from the available shutter speed candidates. Among these icons, a white arrow indicates that there are no candidate shutter speeds, and a black arrow indicates that there are candidate shutter speeds. In Figure 18(a), since there are no other SetPosFlkTv candidates for the first candidate area of ​​selectable shutter speeds 1803, a white arrow icon is displayed next to the first candidate area of ​​selectable shutter speeds 1803n. This is also the case in the example shown in Figure 18(b). In addition, in Figure 18(a), since there is another shutter speed (1 / 180.0) that is highly effective in reducing the effect of flicker for the candidate area of ​​selectable shutter speeds 1805, a black arrow icon is displayed next to the candidate area of ​​selectable shutter speeds 1805. In Figure 18(b), a black arrow icon is displayed next to the candidate range 1805 for selectable shutter speeds because there are other shutter speeds (1 / 135.0) that are highly effective in reducing the effects of flicker.

[0132] As described above, the camera body 100 of this embodiment can notify the user of multiple candidates for shutter speeds that can reduce the effects of flicker, in addition to the arbitrary SetPosFlkTv. With this configuration, for example, the user can easily set their desired shutter speed from among multiple candidates that can reduce the effects of flicker, while reducing the work of manually adjusting the shutter speed to reduce the effects of flicker.Therefore, the camera body 100 according to the present invention can perform imaging with reduced flicker effects across a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operations, and can reduce unevenness in images caused by flicker.

[0133] (Third embodiment) In the first embodiment described above, an example was described in which a specific notification screen is displayed on the display unit 102. In contrast, in this embodiment, a configuration in which flicker detection processing is performed during live view display, which sequentially displays captured images, will be described with reference to Figure 19. Note that the configuration and basic driving method of the camera body 100, lens unit 200, and light-emitting device 300, which are imaging devices according to this embodiment, are substantially the same as those of the first embodiment described above, so the reference numerals for each part are the same and the explanation is omitted.

[0134] Figure 19 is a diagram illustrating an illustrative transition screen to the flicker reduction process during live view display according to the third embodiment of the present invention. In this embodiment, a configuration in which live view display is performed on the display unit 102 is described, but a configuration in which live view display is performed on an electronic viewfinder (not shown) may also be used. During live view display, the image sensor 101 performs sampling (charge accumulation) for flicker detection at a timing different from the charge accumulation timing for obtaining the captured image used for live view display.

[0135] As shown in Figure 19, the flicker detection icon 1901 is an icon display used in the first embodiment described above to indicate that flicker has been detected by the flicker detection process described above. Note that if a different flicker detection process is possible, the icon 1901 may be displayed similarly, or a different icon may be used. Other flicker detection processes could include detecting specific flickers (100Hz, 120Hz) caused by periodic changes in the commercial power supply.

[0136] Furthermore, the icon 1901 may be configured to be displayed only when flicker is detected, or it may be configured to always display the icon and change (update) its display content depending on whether or not flicker is detected. In addition, the CPU 103 may be configured to control the system so that the flicker detection process is executed when the user presses down the flicker detection icon 1901.

[0137] The flicker reduction menu icon 1902 is an icon that, when pressed down by the user (including touch operation), transitions the display content of the display unit 102 to the notification screen described in the first and second embodiments above. In other words, the camera body 100 according to this embodiment allows the user to transition directly to the notification screen during live view display without going through other user interfaces such as a menu screen.

[0138] As described above, the camera body 100 of this embodiment can detect flicker that changes across a wide range of frequencies, even when the subject is being photographed, such as during live view display, and transition to image capture with reduced flicker effects, all with simple operation by the user. This configuration reduces the number of manual operations required by the user for flicker detection, while allowing the user to easily set their desired shutter speed from among multiple candidates that can reduce the effects of flicker. Therefore, the camera body 100 according to the present invention can perform image capture with reduced flicker effects across a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operations, and can reduce unevenness in images caused by flicker.

[0139] (Fourth Embodiment) In the first embodiment described above, the process for determining the exposure time for flicker reduction when the current shutter speed (CurTv) is set in advance was explained. In contrast, this embodiment describes the process for determining the exposure time for flicker reduction when a specific shutter speed (CurTv) is not set, for example, by manual operation by the user. Note that the configuration and basic driving method of the camera body 100, lens unit 200, and light-emitting device 300, which are imaging devices according to this embodiment, are substantially the same as those of the first embodiment described above, so the reference numerals for each part are the same and their descriptions are omitted.

[0140] In addition to the auto mode and manual mode mentioned above, the shooting modes that can be set in the camera body 100 include a priority mode in which the user manually sets an arbitrary exposure control value and other exposure control values ​​are automatically set. As this priority mode, the camera body 100 according to this embodiment can be set to, for example, a shutter speed priority mode in which the user can manually set the shutter speed.

[0141] For example, in an automatic exposure control state where the shooting mode of the camera body 100 is set to auto mode, the user does not set an arbitrary shutter speed. Therefore, in the flicker reduction exposure time determination process in the first embodiment described above, there is little need to determine the ideal flicker reduction exposure time IdealFlkExpTime by considering the current shutter speed CurTv.

[0142] Therefore, in this embodiment, the ideal flicker reduction exposure time, IdealFlkExpTime, is determined based on the determination result regarding whether the current shutter speed, CurTv, is the shutter speed, CurUserTv, that has been manually set by the user. Specifically, in the camera body 100 of this embodiment, the CPU 103 determines whether CurTv ≠ CurUserTv. If the determination determines that CurTv ≠ CurUserTv, the CPU 103 sets the shutter speed with the smallest difference from the ideal flicker reduction exposure time in the shutter speed setting table as the configurable flicker reduction shutter speed.

[0143] If we apply the above-described configuration to the flicker reduction exposure time determination process mentioned earlier, steps S1203 and S1205 onward become unnecessary. In this case, the ideal flicker reduction exposure time, IdealFlkExpTime, will be set to an exposure time that is the reciprocal of the detected flicker light intensity change frequency, but it is not limited to this. For example, as described above in the second embodiment, the configurable flicker reduction shutter speed may be set such that the difference is minimized with respect to a value obtained by multiplying the ideal flicker reduction exposure time by an integer N, in order to maximize the effect of reducing the influence of flicker. In this case, the configurable shutter speeds according to the shutter speed setting table are repeatedly compared with integer multiples of the ideal flicker reduction exposure time, IdealFlkExpTime. Then, the shutter speed with the smallest difference is selected as the configurable flicker reduction shutter speed, SetPosFlkTv.

[0144] For example, in the first and second embodiments described above, the value of the configurable flicker reduction shutter speed SetPosFlkTv was determined by considering the difference with CurTv, assuming that CurTv is set, but it is not limited to this. For example, the camera body 100 may compare the difference with the shutter speed corresponding to each index for each flicker light intensity change frequency and its integer multiple reciprocal, and set the value with the smallest difference as the configurable flicker reduction shutter speed SetPosFlkTv. In this case, the range of flicker light intensity change frequencies that can be reduced by the shutter speeds configurable by the camera body 100 should be defined, and only the reciprocals of frequencies that fall within this range should be used for comparison.

[0145] In this embodiment, the determination of whether or not CurTv ≠ CurUserTv may be made based on the shooting mode currently set in the camera body 100.

[0146] As described above, the camera body 100 of this embodiment can calculate an optimal shutter speed that effectively reduces the effects of flicker that varies across a wide range of frequencies, even when the user has not set a specific shutter speed. With this configuration, the user can easily set the shutter speed that most effectively reduces the effects of flicker, regardless of the shooting conditions of the camera body 100, without requiring any complex operations. Therefore, the camera body 100 according to the present invention can perform imaging that reduces the effects of flicker over a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operations, and can reduce unevenness in images caused by flicker.

[0147] (Fifth embodiment) In the first embodiment described above, the flicker reduction process related to subject imaging when acquiring still images was explained. In contrast, this embodiment describes the flicker reduction process related to subject imaging when acquiring moving images. Note that the configuration and basic driving method of the camera body 100, lens unit 200, and light-emitting device 300, which are imaging devices according to this embodiment, are substantially the same as those of the first embodiment described above, so the reference numerals for each part are the same and their explanations are omitted.

[0148] When acquiring video footage, the available shutter speeds are limited by the update cycle of each frame that makes up the video. In other words, there are shutter speeds that cannot be set depending on the video recording frame rate.

[0149] Furthermore, even among the configurable shutter speeds, some values ​​are undesirable when acquiring moving images. For example, a short shutter speed results in a short exposure time per frame, and the time difference between each frame that makes up the moving image becomes large, causing the subject's movement in the image to appear less smooth.

[0150] Therefore, in this embodiment, for the flicker reduction process when acquiring moving images, the longest exposure time that can be set at the set frame rate of the moving image is set as the ideal flicker reduction exposure time. However, there may be cases where the flicker reduction exposure time and the settable flicker reduction shutter speed do not match. Therefore, if the settable flicker reduction shutter speed selected based on the newly determined ideal flicker reduction exposure time is a value that cannot be set at the current frame rate of the moving image, the settable flicker reduction shutter speed is adjusted. Specifically, among shutter speeds that are not limited by the frame rate of the moving image, the shutter speed closest to the newly determined ideal flicker reduction exposure time is set as the settable flicker reduction shutter speed.

[0151] In this embodiment, the process involving comparison with CurTv in the flicker reduction exposure time determination process described above can be omitted. However, the final ideal flicker reduction exposure time may be the longest exposure time among the ideal flicker reduction exposure times (integer multiples thereof) in which the difference with the current shutter speed CurTv falls within a predetermined range.

[0152] As described above, the camera body 100 of this embodiment can detect flicker that changes over a wide range of frequencies and capture images with reduced flicker effects, while suppressing a decrease in the quality of the moving image even when capturing a subject for acquiring a moving image. With this configuration, the camera body 100 according to this embodiment can easily set a shutter speed that reduces the effects of flicker, both when acquiring still images and moving images, without requiring any additional operation by the user. Therefore, the camera body 100 according to the present invention can perform imaging with reduced flicker effects over a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operation, and can reduce unevenness in images caused by flicker.

[0153] (Sixth Embodiment) In the first embodiment described above, a configuration was described in which the ideal flicker reduction exposure time is set so that the difference from the current shutter speed CurTv is small. In contrast, this embodiment describes a method for setting an ideal flicker reduction exposure time that can reduce the effects of camera shake and subject blur. Note that the configuration and basic driving method of the camera body 100, lens unit 200, and light-emitting device 300, which are imaging devices according to this embodiment, are substantially the same as those of the first embodiment described above, so the reference numerals for each part are the same and the explanation is omitted.

[0154] Generally, longer shutter speeds (exposure times) increase the likelihood of blurred images due to camera shake or subject movement (so-called subject blur). In other words, to reduce blur in images, it is desirable to use the shortest possible shutter speed.

[0155] In the camera body 100 according to this embodiment, in the flicker reduction exposure time determination process according to the first embodiment described above, the ideal flicker reduction exposure time is determined to be shorter than a predetermined exposure time. The predetermined exposure time may be any value that can reduce the effect of motion blur on the subject in the image, but in this embodiment, the predetermined exposure time is exemplified as 1 / 125 seconds.

[0156] In this embodiment, the process of comparing with CurTv in the flicker reduction exposure time determination process described above can be omitted. However, the ideal flicker reduction exposure time may be determined such that the exposure time is shorter than the predetermined exposure time, while the difference between the current shutter speed CurTv and the ideal flicker reduction exposure time (or an integer multiple thereof) falls within a predetermined range.

[0157] Furthermore, the camera body 100 may be configured to set an ideal flicker reduction exposure time that reduces the effect of subject blur when a condition for reducing blur (for example, a specific shooting scene (such as a sports scene)) is set as a shooting condition.

[0158] As described above, the camera body 100 of this embodiment can detect flicker that changes over a wide range of frequencies and take images with reduced flicker effects while suppressing the effect of subject blur in the image. With this configuration, even when specific shooting conditions intended to reduce blur are set, the camera body 100 of this embodiment can easily set a shutter speed that reduces the effect of flicker without requiring any additional operation by the user. Therefore, the camera body 100 according to the present invention can take images with reduced flicker effects over a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operation, and can reduce unevenness in images caused by flicker.

[0159] (Seventh Embodiment) This embodiment describes the flicker reduction process during light emission imaging using the light emission device 300. Note that the camera body 100, lens unit 200, and light emission device 300, which constitute the imaging device according to this embodiment, have substantially the same configuration and basic driving method as those of the first embodiment described above. Therefore, the same reference numerals are used for each part, and their descriptions are omitted.

[0160] In flash photography using the light-emitting device 300, the configurable flicker reduction shutter speed is limited by the synchronization speed, which is determined based on the timing of exposure of the image sensor 101 and the flash timing of the light-emitting device 300. In other words, the camera body 100 according to this embodiment sets the configurable flicker reduction shutter speed from a list of shutter speed candidates that are slower than the synchronization speed of the light-emitting device 300. Specifically, the CPU 103 determines whether or not to perform flash photography using the light-emitting device 300. If it is determined that flash photography will be performed, the CPU 103 limits the selectable shutter speeds in the shutter speed setting table to a range that is slower than the synchronization speed of the light-emitting device 300.

[0161] In this embodiment, the process involving comparison with CurTv in the flicker reduction exposure time determination process described above can be omitted. However, the final ideal flicker reduction exposure time may be the synchronization speed of the light-emitting device 300 that has the smallest difference from the current shutter speed CurTv among the ideal flicker reduction exposure times (integer multiples thereof).

[0162] As described above, the camera body 100 of this embodiment can detect flicker that changes over a wide range of frequencies and take images with reduced flicker effects, while maintaining an appropriately illuminated subject even when taking flash photography using a light-emitting device. With this configuration, the camera body 100 according to this embodiment can easily set a shutter speed that reduces the effects of flicker during flash photography without requiring any additional operation by the user. Therefore, the camera body 100 according to the present invention can take images with reduced flicker effects over a wide range of light intensity change frequencies, regardless of the light source, without requiring complex operations, and can reduce unevenness in images caused by flicker.

[0163] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its essence. For example, in the embodiments described above, a digital camera was assumed as an example of an imaging device for carrying out the present invention, but it is not limited thereto. For example, a configuration may employ an imaging device other than a digital camera, such as a digital video camera, a portable device or wearable terminal such as a smartphone, an in-vehicle camera or a security camera.

[0164] Furthermore, while the above-described embodiment described a configuration that can detect and reduce flicker that changes over a wide range of frequencies without specifying a light source, the system is not limited to this. For example, a configuration may be used in which a specific light source is specified in advance, and flicker is detected in accordance with the frequency range in which it is most likely to occur. In this case, for example, similar to the shutter speed setting table shown in Figure 2, table data may be prepared for each light source (or a similar group of light sources), and the configuration may be used to limit the shutter speed that is most likely to be set for each table data, based on the light intensity change period of the light source. With this configuration, it is possible to efficiently set a shutter speed that can reduce the effect of flicker in accordance with the flicker that is most likely to occur with each light source, thereby effectively reducing the effect of flicker while minimizing the amount of data in the table data.

[0165] Furthermore, in the embodiments described above, the operation of the entire device was controlled by the coordinated operation of each component constituting the imaging system, centered around the CPU 103. However, the system is not limited to this configuration. For example, a (computer) program following the flow shown in the figures described above may be stored in the ROM of the camera body 100 in advance. Then, a microprocessor such as the CPU 103 may execute this program to control the operation of the entire imaging system. Moreover, the form of the program is not limited as long as it has the functionality of a program, such as object code, a program executed by an interpreter, or script data supplied to the OS. Furthermore, the recording medium for supplying the program may be, for example, a hard disk, a magnetic recording medium such as magnetic tape, or an optical / magneto-optical recording medium.

[0166] Furthermore, although the embodiments described above assumed a digital camera as an example of an imaging device for implementing the present invention, the invention is not limited to this. For example, various imaging devices such as digital video cameras, portable devices such as smartphones or wearable terminals, or security cameras may be used in the configuration.

[0167] (Other embodiments) Furthermore, the present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions. [Explanation of Symbols]

[0168] 100 Camera Body 101 Image sensor 102 Display Unit 103 CPU 200 shooting lens 300 Light-emitting devices

Claims

1. An imaging device equipped with an image sensor, A flicker detection means for detecting flicker, which is a periodic change in the amount of light in a subject, A determination means for determining candidate shutter speeds based on the flicker light intensity change frequency detected by the flicker detection means, A means of disseminating information, It has, In the state where a preset shutter speed has been set in advance from among the settable shutter speeds in the aforementioned imaging device, The notification means, if the preset shutter speed does not match any of the shutter speeds that are integer multiples of the reciprocal of the frequency of the flicker light intensity change detected by the flicker detection means, notifies the user of information to allow them to choose whether to change to the candidate shutter speed. The imaging device is characterized in that the candidate shutter speed is the settable shutter speed that is closest to the preset shutter speed among the shutter speeds that are integer multiples of the aforementioned shutter speed.

2. The imaging apparatus according to claim 1, characterized in that the notification means notifies information regarding the pre-set shutter speed.

3. The imaging apparatus according to claim 1 or 2, characterized in that the notification means can notify information regarding the frequency of changes in the light intensity of the flicker detected by the flicker detection means.

4. The imaging apparatus according to any one of claims 1 to 3, wherein the notification means is a display device, and various notifications can be made to the user by displaying a notification screen on the display device.

5. The imaging apparatus according to claim 4, characterized in that the display device is capable of displaying a live view based on a captured image of a subject obtained using the image sensor, and can display the detection result of the flicker detection means on a predetermined icon displayed during the live view display.

6. The imaging apparatus according to claim 5, characterized in that the display device displays the notification screen in response to a user's press operation on the predetermined icon.

7. Having control means for controlling the change of shutter speed, The imaging device according to any one of claims 1 to 6, characterized in that the control means changes the shutter speed set in the imaging device to the candidate shutter speed in response to an instruction from the user to change to the candidate shutter speed.

8. A control method for an imaging device equipped with an image sensor and a notification means, A flicker detection process that detects flicker, which is a periodic change in the amount of light in the subject, A determination step is performed to determine a candidate shutter speed based on the frequency of the change in light intensity of the flicker detected in the flicker detection step, A control step that allows the notification means to provide information regarding the candidate shutter speed, It has, In the control step, if the pre-set shutter speed does not match any of the shutter speeds that are integer multiples of the reciprocal of the flicker light intensity change frequency detected in the flicker detection step, the control is configured to provide the user with information to allow them to choose whether to change to the candidate shutter speed. A method for controlling an imaging device, characterized in that the candidate shutter speed is the shutter speed that is closest to the preset shutter speed among the shutter speeds that are integer multiples of the candidate shutter speed, and is the shutter speed that the imaging device can set closest to the preset shutter speed.

9. A computer-readable program for causing a computer to execute the control method of the imaging device described in claim 8.

Images