Imaging apparatus, control method thereof, and program

Abstract

To prevent a subject image with unnatural brightness from being acquired regardless of imaging scene.SOLUTION: An imaging apparatus includes: first photometry means which divides an image obtained through imaging means and acquires photometric values of multiple regions in a first arithmetic method; second photometry means which acquires photometric values of the regions in a second arithmetic method different from the first arithmetic method; evaluation value calculation means which calculates an evaluation value for determining exposure in imaging a subject; and correction value calculation means which calculates a correction value on the basis of a first photometry result obtained through the first photometry means and a second photometry result obtained through the second photometry means. The second photometry means acquires, for the subject with the same luminance, a photometric value which is equal to or lower than photometric values obtained by the first photometry means for the multiple regions. The evaluation value calculation means is configured to calculate an evaluation value based on the first photometry result and the correction value.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an imaging device, a control method thereof, and a program, and particularly to a photometric method for a subject.

Background Art

[0002] Conventionally, a method for setting an exposure when imaging a subject based on a photometric value obtained by photometrically measuring the subject is known. For example, FIG. 9 is a diagram exemplarily explaining a certain subject image. In the example illustrated in FIG. 9, a screen area corresponding to the shooting angle of view is divided, and a photometric value (average value) is obtained for each area. Then, for example, FIG. 10 is a diagram exemplarily explaining a weighting table for photometric values. As illustrated in FIG. 10, by multiplying the photometric values obtained in each area by an arbitrary weighting table and performing a weighted average, the photometric value of the entire screen can be obtained. In the exemplary photometric weighting table illustrated in FIG. 10, the difference in density within the screen indicates the difference in the degree of weighting (specifically, the weighting coefficient). The darker (darker) part has a lower degree of weighting than the lighter (brighter) part.

[0003] Incidentally, the output with respect to the amount of light incident on a charge accumulation type solid-state imaging device (sensor) such as a CCD or a CMOS sensor is a physical signal amount whose output is linear with respect to the input, but it is known that there is a difference from the sensory amount perceived by humans. Generally, the amount of light that the human eye perceives as an appropriate brightness is smaller than the intermediate value of the output obtained by linearly converting the amount of light incident on the sensor.

[0004] For example, FIG. 11 is a diagram exemplarily explaining a backlight scene where the background is of high brightness with respect to a building as the main subject. In the backlight scene illustrated in FIG. 11, when simply performing average photometry of the entire screen, there is a risk that imaging may be performed with an exposure (so-called underexposure) in which the building as the main subject becomes dark due to the influence of the bright area of the sky as the background. FIG. 12 shows this state and is a diagram exemplarily explaining the case where the building is imaged in an underexposed state in a backlight scene. Thus, due to differences in the main subject and changes in the shooting environment, there may be cases where the photometry result desired by the user cannot be obtained.

[0005] Regarding such problems, for example, a method is known in which sensor output is logarithmically transformed (logarithmic compression) to increase the gradation of the low-brightness area and compress the gradation of the high-brightness area, thereby obtaining image data that matches the perception of the human eye. For example, in Patent Document 1, a technique is proposed in which photometric values of a photometric sensor having a plurality of photometric areas are logarithmically transformed, and a composite photometric output is calculated using a correction value according to the difference in logarithmic values between different areas (the central part and its peripheral part).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when logarithmically transforming the photometric value, since the high-brightness area is compressed and output, there is a risk that the gradation of the high-brightness area may decrease when the main subject is of high brightness. Therefore, in the technique described in Patent Document 1, for example, when the main subject is located in the central part of the screen and there is a low-brightness subject in the peripheral part with respect to the central part, there is a risk that the main subject may not have an appropriate brightness according to the photometric result. In particular, this problem becomes prominent when the low-brightness area is wide with respect to the entire area used for photometry.

[0008] For such a shooting scene, by using the photometric value obtained by linearly converting the sensor output, the main subject can be set to an appropriate brightness. However, there are still shooting scenes that are difficult as described above for the photometric value obtained by linearly converting the sensor output. That is, depending on the shooting scene, there are cases where it is preferable to linearly convert the sensor output and cases where it is preferable to logarithmically convert the sensor output. The object of the present invention is to provide a photometric method capable of preventing the subject from having an unnatural brightness regardless of the shooting scene.

Means for Solving the Problems

[0009] To solve the above problems, an imaging device according to the present invention includes imaging means for imaging a subject and outputting an image, first photometric means for dividing the image obtained by using the imaging means into a plurality of regions and obtaining photometric values of the plurality of regions by a first calculation method, second photometric means for dividing the image obtained by using the imaging means into a plurality of regions and obtaining photometric values of the plurality of regions by a second calculation method different from the first calculation method, evaluation value calculation means for calculating an evaluation value for determining an exposure when imaging a subject, and correction value calculation means for calculating a correction value based on a difference value between a first photometric result obtained by using the first photometric means and a second photometric result obtained by using the second photometric result. The second photometric means obtains a photometric value that is equal to or less than the photometric value obtained by the first photometric means for the plurality of regions when the luminance of the subject is the same. The evaluation value calculation means calculates the evaluation value based on the first photometric result and the correction value.

Effects of the Invention

[0010] According to the present invention, it is possible to prevent the subject from having an unnatural brightness regardless of the shooting scene.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Mode for Carrying Out the Invention

[0012] (First Embodiment) (Basic Configuration of Camera System 1) Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a block diagram for explaining the configuration of a camera system 1 including an imaging device 100 according to a first embodiment of the present invention. Further, FIG. 2 is a schematic configuration diagram of the camera system 1 including the imaging device 100 according to the first embodiment of the present invention. Note that one or more of the functional blocks shown in FIGS. 1 and 2 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, in the following description, even when different functional blocks are described as the operating entity, the same hardware may be realized as the main body.

[0013] The overall control unit 101 is composed of an arithmetic device such as a CPU (Central Processing Unit), is connected to each block described later, and is a control means capable of comprehensively controlling the imaging device 100 and each part mounted on the imaging device 100. A memory unit 109 having a ROM area and a RAM area is connected to the overall control unit 101. Among these, the ROM area is a non-volatile recording element, and stores programs for operating the overall control unit 101 and various adjustment parameters. The program read from this ROM area is expanded and executed in the RAM area which is a volatile recording element. Note that the RAM area is a so-called frame memory, which is a storage unit capable of temporarily storing an image signal and reading it out when necessary.

[0014] The interchangeable lens 200 is a lens unit detachable from the imaging device 100, and includes various lens groups 202, an aperture 204 for guiding a light beam indicating an optical image of a subject into the imaging device 100, a lens driving unit 203 for driving these, and an aperture driving unit 205. The lens control unit 201 is a control means for comprehensively controlling the operations of each part included in the interchangeable lens 200, and by being connected to the overall control unit 101 of the imaging device 100 described above, various information can be exchanged between both the imaging device 100 and the interchangeable lens 200.

[0015] The QR mirror 102 is a quick return (QR) mirror, and is an optical system for guiding the optical image of the subject incident inside the imaging device 100 to either the viewfinder 123 and the photometric imaging element (imaging element B) 116 side or the imaging element (imaging element A) 106 side. The QR mirror 102 includes a so-called surf mirror and a sub mirror. In the mirror-down state, the optical image of the subject is guided to the photometric imaging element 116 side and the AF sensor 121 side, and in the mirror-up state, the optical image of the subject is guided to the imaging element 106 side. The QR mirror driving unit 103 is a driving means for driving the QR mirror 102.

[0016] The pentaprism 119 is an optical system for guiding the light beam of the subject guided in the mirror-down state of the QR mirror 102 to the viewfinder 123 and the imaging element 116. Note that the light beam guided to the imaging element 116 is guided to the imaging element 116 via the photometric optical system 122 and the bending optical system 124.

[0017] The shutter mechanism 104 is a shutter mechanism having shutter curtains corresponding to a so-called focal plane type front curtain / rear curtain, and adjusts the exposure time and light-shielded state of the light incident on the imaging element A. The shutter driving unit 105 is a shutter driving means for driving the shutter mechanism 104.

[0018] The imaging element 106 (imaging element A) is an imaging means employing a charge accumulation type solid imaging element such as a CMOS that can receive the light beam of the subject guided by the lens group 202 and convert it into an electrical image signal.

[0019] The signal processing unit 107 (signal processing unit A) is an imaging processing means that performs various processes on the image signal output from the imaging element 106. For example, the signal processing unit 107 executes amplification processing of the image signal, A / D conversion processing for converting an analog signal into a digital signal, various correction processes such as defect correction for the image signal after A / D conversion, and compression processing for compressing the image signal.

[0020] The timing generation unit 108 (timing generation unit A) is a timing generation means that outputs a timing signal for adjustment when executing various operations for the imaging element 106 and the signal processing unit 107.

[0021] The recording medium IF 110 is an interface unit for performing recording processing of an image signal and the like on the recording medium 111 connectable to the imaging device 100, and reading processing of an image signal and the like from the recording medium 111. The recording medium 111 is a recording medium composed of a semiconductor memory or the like that records various data such as an image signal, and is detachable from the imaging device 100.

[0022] The display driving unit 112 is a display driving means that drives a display device 113 that converts and displays an image signal obtained by imaging a subject for display. The external IF 114 is an external interface unit that controls the transmission and reception of information such as an image signal and a control signal with an external device such as a computer 115, for example.

[0023] The imaging element 116 (imaging element B) is an imaging element for acquiring a photometric signal (photometric value) of a subject mainly used for exposure control, and like the imaging element 106, employs a charge accumulation type solid-state imaging element such as a CMOS. Note that the imaging element 116 of the present embodiment includes pixels for IR (infrared) detection in addition to RGB pixels based on a so-called Bayer array. As an operation using the imaging element 116, it is possible to acquire a light source detection signal and a flicker right signal in addition to photometry of a subject, but the description thereof is omitted.

[0024] The signal processing unit 117 (signal processing unit B) is an imaging processing means that performs various processes on the image signal output from the imaging element 116. Since the content of the process is substantially the same as that of the signal processing unit 107 described above, the description thereof is omitted. Further, the timing generation unit 118 (timing generation unit B) is a timing generation means that outputs a timing signal for adjustment when executing various operations for the imaging element 116 and the signal processing unit 117. The above is the basic configuration of the camera system 1.

[0025] (Exposure value correction process) With reference to FIGS. 3 to 5, the photometric process according to the first embodiment of the present invention will be described. FIG. 3 is a flowchart showing each sequence of the photometric process according to the first embodiment of the present invention. The photometric process of the present embodiment includes a correction value calculation process and an exposure value correction process. Further, the photometric process is started at the time of power-on of the imaging device 100, at the time of an imaging instruction for a subject, or at a regular photometric timing during so-called live view on the display device 113, but it may be configured to be started at an arbitrary timing by the user.

[0026] When the photometric process is started, as shown in FIG. 3, in step S101, the overall control unit 101 calculates a linear photometric value obtained by linearly converting the output with respect to the subject image (input) incident on the imaging element 116, and a logarithmic photometric value obtained by logarithmic conversion (logarithmic compression), respectively. The linear photometric value (linear photometric value) and the logarithmic photometric value (logarithmic photometric value) are representative photometric values of the entire screen obtained by calculation methods using different conversion characteristics. Specifically, in the present embodiment, the entire screen corresponding to the imaging element 116 is divided into a plurality of regions, and for each pixel, luminance values obtained by linear conversion and logarithmic conversion are obtained, and for each divided region, an integrated value of the luminance values of each pixel is obtained to obtain an average luminance value for each divided region. Then, the additive average value of each linearly converted divided region is used as the linear photometric value, and the additive average value of each logarithmically converted divided region is used as the logarithmic photometric value. Generally, the logarithmic photometric value has a conversion characteristic (compression method) such that the luminance level output from the imaging element is less than or equal to the luminance level input to the imaging element with respect to the linear photometric value.

[0027] In this embodiment, the case where the average luminance values for each divided area are additively averaged over the entire screen has been described. However, a configuration may also be adopted in which the degree of weighting is made different for each area, and each photometric value is obtained by weighted averaging the degree of weighting and the average photometric value. Also, the units of the luminance value and the photometric value are assumed to be such that 1 EV in the so-called APEX (ADDITIVE SYSTEM OF PHOTOGRAPHIC EXPOSURE) system corresponds to one step of the luminance value and the photometric value, based on the logarithmically transformed state.

[0028] Next, in step S102, the overall control unit 101 executes a correction value calculation process for photometry using the logarithmic photometric value and the linear photometric value calculated in step S101. Details of the correction value calculation process will be described later.

[0029] Next, in step S103, the overall control unit 101 executes a photometric value correction process based on the linear photometric value calculated in step S101 and the correction value for photometry calculated in step S102. Details of the photometric value correction process will be described later. Then, in accordance with the final photometric value obtained through the photometric value correction process, an exposure suitable for the photometric value is determined from the previously determined exposure conditions for exposure control, and imaging of the subject is performed.

[0030] FIG. 4 is a flowchart showing each sequence of the correction value calculation process according to the first embodiment of the present invention, and corresponds to the process in step S102 in the photometric process described above. Hereinafter, the correction value calculation process according to the present embodiment will be described with reference to FIGS. 4 and 6 to 8.

[0031] When the correction value calculation process is started, first, in step S201, the overall control unit 101 obtains a difference value between the linear photometric value and the logarithmic photometric value calculated in the previous step S101. Specifically, in this embodiment, the difference value is calculated by subtracting the logarithmic photometric value from the linear photometric value, but a configuration may also be adopted in which the absolute value of the difference between the linear photometric value and the logarithmic photometric value is obtained.

[0032] Here, FIG. 6 is a diagram exemplarily explaining how the logarithmic photometry value and the linear photometry value change according to the difference in luminance difference between different regions across the entire screen. The luminance values and photometry values indicated by each line are as shown in FIG. 6. In FIG. 6, for example, it is assumed that while the luminance (first luminance) of the background, which is the first region across the entire screen, changes, the luminance (second luminance) of the main subject region, which is the second region, remains constant without changing. Therefore, in FIG. 6, the difference between the background luminance and the subject luminance increases towards the right side in the figure. In particular, in the region 601 indicated by the dashed line, the difference between the two becomes large. Note that in FIG. 6, one grid represents a difference of approximately 1 EV, and the vertical axis indicates the output luminance with respect to the input luminance indicated by the horizontal axis.

[0033] As shown in FIG. 6, when the luminance difference across the entire screen increases due to an increase in the first luminance (background luminance), the linear photometry value increases at approximately the same rate as the first luminance, while the logarithmic photometry value increases at a lower rate than the change in the first luminance. In other words, when the luminance transitions to the high-luminance side, the greater the luminance difference across the entire screen, the greater the difference between the linear photometry value and the logarithmic photometry value. Therefore, for example, in a shooting scene as shown in FIG. 11, when performing exposure control based on the linear photometry value, the influence of the background brightness is large and the building becomes dark, whereas with exposure control based on the logarithmic photometry value, the influence of the background brightness is small and the darkening of the building can be suppressed. Thus, in a shooting scene where a high-luminance subject exists, when the low-luminance subject is the main subject, the logarithmic photometry value makes it easier for the main subject to have an appropriate brightness compared to the linear photometry value.

[0034] However, even when there is a large luminance difference across the entire screen, for example, when the high-luminance subject is the main subject, the linear photometry value is more likely to result in the main subject having an appropriate brightness than the logarithmic photometry value. For example, FIG. 13 is a diagram exemplarily explaining a shooting scene where the main subject is a high-luminance subject and the background is low-luminance. In a case as illustrated in FIG. 13, it is more likely that the main subject will have an appropriate brightness when determining the exposure based on the linear photometry value. Generally, the probability that the main subject is high-luminance is higher than when it is low-luminance. Therefore, when determining the exposure according to various shooting scenes, there is a tendency that determining the exposure based on the linear photometry value is more likely to result in an appropriate brightness for the shooting scene. However, in some shooting scenes as described above, it may be more suitable to use the logarithmic photometry value.

[0035] Therefore, in the present embodiment, in order to obtain a photometry value for determining the exposure, both the linear photometry value and the logarithmic photometry value of the entire screen are calculated, and the linear photometry value is corrected in view of the value of the logarithmic photometry value, thereby calculating an optimal photometry value regardless of the shooting scene. The details will be described below.

[0036] Returning to FIG. 4, in step S202, the overall control unit 101 determines whether the difference value obtained in step S201 is smaller than a first threshold value (threshold value 1). And when it is determined that the difference value is equal to or greater than the threshold value 1 (NO in step S202, equal to or greater than the first threshold value), in step S203, the overall control unit 101 determines whether the difference value obtained in step S201 is greater than a second threshold value (threshold value 2). Here, FIG. 7 is a diagram exemplarily explaining a method for calculating a first correction value for the photometry value according to the first embodiment of the present invention. In FIG. 7, the horizontal axis represents the magnitude of the difference value (unit: EV), and the difference increases as moving to the right. The vertical axis represents the degree of the first correction value (unit: EV), and the degree of correction increases as moving downward.

[0037] As shown in FIG. 7, when the difference value between the linear photometry value and the logarithmic photometry value is small, it is considered that the luminance difference across the screen is small. Therefore, in the present embodiment, when the difference value is smaller than threshold value 1 (NO in step S202), the process proceeds to step S206, and the overall control unit 101 sets the first correction value to 0 and does not correct the photometry value.

[0038] On the other hand, when the difference value between the linear photometry value and the logarithmic photometry value is large, it is considered that the luminance difference across the screen is large. Therefore, in the present embodiment, when the difference value is equal to or greater than threshold value 2 (NO in step S203), the process proceeds to step S205, and the overall control unit 101 sets the first correction value to the minimum value that can be set. Since the first correction value is a correction to the underexposed side with respect to the linear photometry value, when the first correction value is the minimum value, the degree of correction is the maximum.

[0039] When the difference value is equal to or less than the second threshold value (the difference value is between threshold value 1 and threshold value 2), in step S204, the overall control unit 101 linearly interpolates the first correction values corresponding to threshold value 1 and threshold value 2 based on the graph shown in FIG. 7 to obtain the first correction value corresponding to the difference value. Note that table data of the first correction value corresponding to the difference value may be stored in advance in the memory unit 109, and the first correction value may be calculated based on the table data.

[0040] After calculating the first correction value by the method described above, in steps S207 to S211, an attenuation coefficient γ to be multiplied by the first correction value is calculated. FIG. 8 is a diagram exemplarily explaining a method for calculating the attenuation coefficient γ for photometry value correction according to the first embodiment of the present invention. In FIG. 8, the horizontal axis represents the magnitude of the linear photometry value (unit: EV), and the higher the luminance is as it goes to the right, and the vertical axis represents the ratio of the attenuation coefficient γ.

[0041] As described above, since the first correction value is configured such that the degree of correction increases as the difference value between the linear photometry value and the logarithmic photometry value increases, when the main subject is a low-luminance subject, the brightness of the main subject can be made closer to appropriate. However, in a scene where the entire screen is dark, if the linear photometry value is corrected based on the first correction value, the main subject may become darker. For example, it is assumed that the subject is illuminated by a spotlight and the background is dark, or that a point light source such as an electric lamp exists within the screen during night-time outdoor photography. In such cases, since there is a high-luminance area within the screen, the linear photometry value becomes high, but since there are many appropriate areas in the entire screen, the logarithmic photometry value tends to be low, so the luminance difference between the two increases. And in such a case, if the linear photometry value is corrected based on the first correction value, for example, when photographing a spotlight, the main subject in the high-luminance area becomes dark, and in night-time photography, an image that is unnaturally bright with respect to the actual ambient illuminance is obtained.

[0042] Therefore, in the present embodiment, a configuration is adopted in which the linear photometry value is corrected based on the second correction value β obtained by multiplying the first correction value by the attenuation coefficient γ. And the attenuation coefficient γ is made smaller as the linear photometry value is smaller (that is, the entire image is darker), so that the degree of correction of the second correction value after multiplying by the attenuation coefficient γ becomes smaller. The following formula (1) is a formula for calculating the second correction value β described later, and in this formula, the first correction value described above is α. Second correction value β = γ × First correction value α ···(1) According to formula (1), for example, when the attenuation coefficient γ is 0, the second correction value β is also 0, and the linear photometry value does not change (is not corrected) before and after correction. On the other hand, according to formula (1), as the attenuation coefficient increases, the degree of correction of the second correction amount β increases.

[0043] Therefore, in the present embodiment, even if the luminance difference across the entire screen is large and the degree of the first correction value is at its maximum, it is possible to suppress the correction such that the photometric value becomes unnecessarily dark in a scene where the entire screen is dark. According to the present embodiment, in a scene where the luminance difference across the entire screen is large and the entire screen is not dark, it is possible to effectively suppress the subject from being underexposed.

[0044] Returning to FIG. 4, in step S207, the overall control unit 101 determines whether the linear photometric value obtained in step S101 is smaller than a third threshold value (threshold value 3). When it is determined that the linear photometric value is smaller than threshold value 3 (YES in step S207), the attenuation coefficient γ with respect to the first correction value is set to 0.

[0045] When it is determined that the linear photometric value is equal to or greater than threshold value 3 (NO in step S207), in step S208, the overall control unit 101 determines whether the linear photometric value obtained in step S101 is greater than a fourth threshold value (threshold value 4). When it is determined that the linear photometric value is equal to or greater than threshold value 4 (YES in step S208), the attenuation coefficient γ with respect to the first correction value is set to 1.

[0046] When the linear photometric value is between threshold value 3 and threshold value 4, in step S209, the overall control unit 101 obtains the attenuation coefficient γ corresponding to the linear photometric value by linearly interpolating the attenuation coefficients γ corresponding to threshold value 3 and threshold value 4 based on the graph shown in FIG. 8. Note that a configuration may be adopted in which table data of the attenuation coefficient γ corresponding to the linear photometric value is stored in the memory unit 109 in advance, and the attenuation coefficient γ is calculated based on the table data.

[0047] Finally, in S212, the overall control unit 101 calculates a second correction value β from Equation (1) based on the first correction value α obtained in steps S204 to S206 and the attenuation coefficient γ obtained in steps S209 to S211. The above is the correction value calculation process according to the present embodiment. Note that the processes in steps S207 to S211 are processes for improving the accuracy of correcting the linear photometry value in an optimal shooting scene, and a configuration in which the processes in steps S207 to S211 are not executed may be adopted. In this case, in terms of the control algorithm of the imaging device 100, control may be performed so that the second correction value is the same as the first correction value. When this configuration is adopted, there is a possibility that a high-brightness subject may be underexposed. However, if the degree of the problem and the frequency of occurrence of the problem are low, it is sufficiently effective to solve the problem of the present invention by simply calculating the first correction value without performing the processes in steps S207 to S211.

[0048] Next, the photometry value correction process according to the present embodiment will be described with reference to FIG. 5. FIG. 5 is a flowchart showing each sequence of the photometry value correction process according to the first embodiment of the present invention, and corresponds to the process in step S103 in the above-described photometry process.

[0049] First, in step S301, the overall control unit 101 determines whether the selection method (mode) of the distance measurement point (distance measurement area) currently set in the imaging device 100 is the automatic selection method. If it is determined that the selection method of the distance measurement point is the automatic selection method (YES in step S301), the process proceeds to step S302. If it is determined otherwise (NO in step S301), the process proceeds to step S305.

[0050] In step S305, the overall control unit 101 determines that there is no correction of the photometric value, and sets the second correction value described above not to correct the linear photometric value. For example, when the user manually sets the distance measurement point selection method (i.e., the distance measurement point), the photometric value may be determined according to the distance measurement point selected by the manual operation of the user. In this case, if the imaging device 100 automatically corrects the linear photometric value, there is a risk of obtaining a photometric result unintended by the user. Therefore, by controlling not to correct the linear photometric value when the distance measurement point selection method is not automatic selection according to the determination in step S301, it is possible to suppress the occurrence of a photometric result unintended by the user.

[0051] Next, in step S302, the overall control unit 101 determines whether the subject distance to the main subject is equal to or greater than a predetermined value. If it is determined in step S302 that the subject distance to the main subject is less than or equal to the predetermined value, the process proceeds to step S304. If it is determined that the subject distance to the main subject is greater than the predetermined value, the process proceeds to step S303.

[0052] Generally, when the distance to the subject is short, the area ratio occupied by the subject in the entire screen also increases. In this case, since a linear photometric value corresponding to the subject having a high occupancy rate in the entire screen is obtained, the necessity of correcting the photometric value is low. In step 302, this point is determined, and it is possible to suppress the unnatural correction of the photometric value for the subject having a high occupancy rate in the entire screen.

[0053] Note that any known method may be adopted as the method for detecting the main subject in step S302. For example, a configuration may be adopted in which a subject is detected using a subject detection technique such as pattern matching or contrast matching. In addition to this, a configuration may be adopted in which a subject having a high ratio in the entire screen is set as the main subject.

[0054] Also, in the process of step S302, the distance to the main subject was determined, but it is not limited to this. For example, as the process of step S302, a determination method of comparing the shooting magnification with a predetermined value may be used, or a method of determining the ratio of the subject occupying the entire screen may be used.

[0055] Next, in step S303, the overall control unit 101 determines whether or not a face area exists within the screen. Depending on the determination in step S303, if it is determined that a face area exists, the process proceeds to step S305, and if it is determined that no face area exists, the process proceeds to step S304. When a face area exists within the screen, by calculating the photometric value according to the face area, the possibility of obtaining an image with the brightness intended by the user is increased. Therefore, depending on the determination in step S303, when a face area exists within the screen, control is performed so as not to correct the linear photometric value, effectively suppressing the acquisition of an image with a brightness unintended by the user.

[0056] Note that any known method may be adopted as the method for detecting the face area in step S303. Also, the order of the processes in steps S302 and S303 is not limited to the order described above. For example, a configuration in which the process of step S303 is executed first may be used. Furthermore, since the photometric value correction process executed in this embodiment is a process for determining the conditions under which the photometric value can be effectively corrected by the second correction value calculated in the correction value calculation process, a configuration in which the photometric value correction process itself is not executed may also be used. The accuracy of obtaining an image with the brightness intended by the user is higher when the photometric value correction process is executed than when it is not executed.

[0057] Based on the determination results of steps S301 to S303 described above, when proceeding to step S304, the overall control unit 101 performs correction on the linear photometry value based on the second correction value described above, and calculates the final photometry value. That is, the overall control unit 101 (evaluation value calculation means) calculates the final photometry value as the evaluation value for determining the exposure when imaging the subject to obtain an image. Note that when proceeding to step S305, since the correction of the linear photometry value is not performed as described above, the linear photometry value calculated in step S101 is used as the final photometry value.

[0058] The above is the photometry value correction process according to this embodiment. After the photometry value correction process is completed, the exposure is determined based on the obtained final photometry value (final photometry value), and the subject is imaged based on the exposure, so that an image with appropriate brightness for the subject can be obtained regardless of the shooting scene.

[0059] Note that as the order of the processes of steps S102 and S103 in FIG. 3 described above, a configuration in which the process of step S103 is executed first may be employed. In this case, it is only necessary to execute the photometry value calculation process only when proceeding to the process of step S304 in the photometry value correction process to calculate the final photometry value. In other words, when proceeding to the process of step S305 in the photometry value correction process, the final photometry value may be determined without executing the photometry value calculation process. In this case, the processing load of the imaging device 100 can be reduced without performing the calculation process of unnecessary correction values.

[0060] The preferred embodiments of the present invention have been described above, but the present invention is not limited to these, and various modifications and changes are possible within the scope of the gist thereof. For example, in the above-described embodiment, an imaging device integrally provided with an optical lens has been described, but a lens interchangeable imaging device to which a so-called interchangeable lens can be attached and detached may be employed.

[0061] In addition, in the above-described embodiments, although the application of the correction value to the linear photometric value was mentioned, the present invention is not limited thereto, and a configuration may be adopted in which the correction value is applied to the logarithmic photometric value. For example, although a backlight scene was exemplified as a shooting scene in which correction of the linear photometric value is necessary, as a shooting scene in which correction of the logarithmic photometric value is necessary, the case where the main subject is high in brightness and the background is low in brightness, such as the above-described spotlight shooting, corresponds thereto.

[0062] In the case of spotlight shooting, if the exposure is determined based on the logarithmic photometric value, there is a risk that the main subject illuminated by the spotlight will be overexposed and saturated due to the influence of the low-brightness area of the background.

[0063] Therefore, in a configuration in which the exposure is determined based on the logarithmic photometric value, as described above, a configuration may be adopted in which the difference value between both the logarithmic photometric value and the linear photometric value is obtained, and the logarithmic photometric value is corrected according to the magnitude of the difference value and the logarithmic photometric value. Specifically, the first correction value α described above with reference to FIG. 7 is determined based on table data in which the plus and minus are reversed compared to the first embodiment described above. In this case, as the difference value increases, the first correction value becomes the maximum value, and the degree of correction becomes the maximum. Therefore, the photometric value is corrected so that the exposure becomes brighter in a dark shooting scene.

[0064] In addition, the attenuation coefficient γ may be determined so that the attenuation rate with respect to the first correction value becomes high (the degree of correction becomes small) when the logarithmic photometric value is bright. For example, it may be determined based on table data in which the relationship between the threshold value and the attenuation coefficient in FIG. 8 described above is reversed.

[0065] In the above-described embodiments, linear photometric values and logarithmic photometric values have been mentioned as the photometric values to be calculated. However, as an embodiment of the present invention, any configuration can be applied as long as it acquires separate photometric values based on two different methods in which the characteristics of the output with respect to the input to the imaging device are different. For example, as the input-output characteristics, if the configuration is to obtain photometric values in which the slopes of the conversion characteristics with respect to the conversion characteristics with a linear conversion of 1:1 output with respect to the input are different, the present invention can be applied. In this case, depending on whether the conversion characteristic is steep or gentle with respect to the photometric value obtained based on the conversion characteristic to be corrected, the direction of the correction value with respect to the difference value (which may be an absolute value) (under-exposure side or over-exposure side) changes.

[0066] Also, in the above-described embodiments, the configuration for calculating the photometric value using the imaging device 116 has been described, but the present invention is also applicable when the photometric value is calculated using the imaging device 106. That is, the present invention is applicable even in a configuration having only an imaging device for acquiring an image signal for recording.

[0067] In the above-described embodiments, the present invention has been described assuming a digital camera as an example of the imaging device for implementing the present invention, but the present invention is not limited thereto. For example, a configuration employing an imaging device other than a digital camera, such as a portable device such as a digital video camera or a smartphone, a wearable terminal, an in-vehicle camera, or a security camera, may be used.

Explanation of Reference Numerals

[0068] 1 Camera system 100 Imaging device 101 Overall control unit 106 Imaging device A 116 Imaging device B 200 Interchangeable lens

Claims

1. Imaging means for imaging a subject and outputting an image, First photometry means for dividing an image obtained by using the imaging means into a plurality of regions and acquiring photometry values of the plurality of regions by linear photometry, Second photometry means for dividing an image obtained by using the imaging means into a plurality of regions and acquiring photometry values of the plurality of regions based on logarithmic photometry or photometry methods having different slopes of deformation characteristics with respect to the conversion characteristics of the linear photometry, Evaluation value calculation means for calculating an evaluation value for determining an exposure when imaging a subject, Correction value calculation means for calculating a correction value based on a difference value between a first photometry result obtained by using the first photometry means and a second photometry result obtained by using the second photometry means, characterized by comprising: When the luminance of the subject is the same, the second photometry means acquires photometry values that are equal to or less than the photometry values acquired by the first photometry means for the plurality of regions, The evaluation value calculation means calculates the evaluation value based on the first photometry result and the correction value. An imaging device characterized by this.

2. The correction value calculation means calculates a first correction value based on the difference value, The imaging device according to claim 1, wherein the calculation is performed such that the first correction value is larger when the difference value is equal to or greater than a first threshold value than when the difference value is smaller than the first threshold value.

3. The imaging device according to claim 2, wherein the correction value calculation means performs the calculation such that the first correction value is larger when the difference value is greater than a second threshold value that is greater than the first threshold value than when the difference value is equal to or less than the second threshold value.

4. The imaging device according to claim 3, wherein when the difference value is equal to or greater than the first threshold value and equal to or less than the second threshold value, the first correction value is the first correction value set when the difference value is smaller than the first threshold value and the first correction value set when the difference value is greater than the second threshold value, and the calculation is performed such that the value is between them.

5. The correction value calculation means calculates a second correction value by multiplying the first correction value by an attenuation coefficient corresponding to the first photometry result, The imaging device according to any one of claims 2 to 4, wherein the evaluation value calculation means calculates the evaluation value based on the first photometry result and the second correction value.

6. The first photometric result and the second photometric result are photometric values indicated by the luminance value of the subject, and the correction value calculation means sets the attenuation coefficient closer to 0 as the first photometric result is a smaller photometric value, and sets the attenuation coefficient closer to 1 as the first photometric result is a larger photometric value, and calculates the second correction value. The imaging device according to claim 5, characterized in that.

7. When the evaluation value calculation means is set to a method in which a distance measurement area is selected by a manual operation of the user in the imaging device, the evaluation value is calculated regardless of the correction value. The imaging device according to any one of claims 1 to 6, characterized in that.

8. When the area of the main subject occupying the entire screen is larger than a predetermined value, the evaluation value calculation means calculates the evaluation value based on the first photometric result and the correction value. The imaging device according to any one of claims 1 to 7, characterized in that.

9. When a face area is included in the screen, the evaluation value calculation means calculates the evaluation value regardless of the correction value. The imaging device according to any one of claims 1 to 8, characterized in that.

10. The logarithmic photometry has a conversion characteristic of logarithmically compressing the photometric values of the plurality of areas. The imaging device according to any one of claims 1 to 9, characterized in that.

11. Imaging means for imaging a subject and outputting an image; First photometric means for dividing the image obtained by using the imaging means into a plurality of areas and acquiring photometric values of the plurality of areas by linear photometry; Second photometric means for dividing the image obtained by using the imaging means into a plurality of areas and acquiring photometric values of the plurality of areas based on logarithmic photometry or a photometry method having a different slope of the deformation characteristic with respect to the conversion characteristic of the linear photometry; Evaluation value calculation means for calculating an evaluation value for determining an exposure when imaging a subject; Correction value calculation means for calculating a correction value based on a difference value between a first photometric result obtained by using the first photometric means and a second photometric result obtained by using the second photometric means; And having When the luminance of the subject is the same, the second photometric means acquires a photometric value that is equal to or less than the photometric value acquired by the first photometric means for the plurality of areas. The evaluation value calculation means calculates the evaluation value based on the second photometric result and the correction value. An imaging device characterized by that.

12. A control method for an imaging device including imaging means for imaging a subject and outputting an image, A first photometry step of dividing an image obtained using the imaging means into a plurality of regions and acquiring photometry values of the plurality of regions by linear photometry; A second photometry step of dividing an image obtained using the imaging means into a plurality of regions and acquiring photometry values of the plurality of regions based on logarithmic photometry or photometry methods having different slopes of deformation characteristics with respect to the conversion characteristics of the linear photometry; An evaluation value calculation step of calculating an evaluation value for determining an exposure when imaging a subject; A correction value calculation step of calculating a correction value based on a difference value between a first photometry result obtained in the first photometry step and a second photometry result obtained in the second photometry step; comprising; In the second photometry step, when the luminance of the subject is the same, photometry values that are equal to or lower than the photometry values acquired in the first photometry step for the plurality of regions are acquired; An imaging device control method, wherein in the evaluation value calculation step, the evaluation value is calculated based on the first photometry result and the correction value.

13. An imaging device control method comprising an imaging means for imaging a subject and outputting an image, A first photometry step of dividing an image obtained using the imaging means into a plurality of regions and acquiring photometry values of the plurality of regions by linear photometry; A second photometry step of dividing an image obtained using the imaging means into a plurality of regions and acquiring photometry values of the plurality of regions based on logarithmic photometry or photometry methods having different slopes of deformation characteristics with respect to the conversion characteristics of the linear photometry; An evaluation value calculation step of calculating an evaluation value for determining an exposure when imaging a subject; A correction value calculation step of calculating a correction value based on a difference value between a first photometry result obtained in the first photometry step and a second photometry result obtained in the second photometry step; comprising; In the second photometry step, when the luminance of the subject is the same, photometry values that are equal to or lower than the photometry values acquired in the first photometry step for the plurality of regions are acquired; An imaging device control method, wherein in the evaluation value calculation step, the evaluation value is calculated based on the second photometry result and the correction value.

14. A computer-readable program for causing a computer to execute the imaging device control method according to claim 12 or 13.

Images