JP2021027407A - Imaging apparatus, control method of the same, program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a subject unnaturally bright regardless of a shooting scene. SOLUTION: A first photometric means for dividing an image obtained by using an imaging means and acquiring photometric values of a plurality of regions by a first calculation method, and a second calculation different from the first calculation method. Using a second photometric means for acquiring photometric values of the plurality of regions by a method, an evaluation value calculating means for calculating an evaluation value for determining exposure when imaging a subject, and a first photometric means. It has a correction value calculation means for calculating a correction value based on the difference value between the obtained first photometric result and the second photometric result obtained by using the second photometric result, and the second calculation. In the method, when the brightness of the subject is the same, the photometric values of a plurality of regions are acquired so that the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. The evaluation value calculation means is characterized in that the evaluation value is calculated based on the first photometric result and the correction value. [Selection diagram] Fig. 4

Description

The present invention relates to an image pickup apparatus, a control method and a program thereof, and particularly to a photometric method of a subject.

Conventionally, there has been known a method of setting an exposure when photographing a subject based on a photometric value obtained by metering the subject. For example, FIG. 9 is a diagram for exemplifying a certain subject image, and in the example shown in FIG. 9, the screen area corresponding to the shooting angle of view is divided, and the photometric value (average value) is measured in each area. Ask for. Then, for example, FIG. 10 is a diagram illustrating an exemplary weighting table for the photometric values, and as shown in FIG. 10, the photometric values obtained in each region are multiplied by an arbitrary weighting table. By performing weighted averaging, the photometric value of the entire screen can be obtained. In the exemplary weighting table for light measurement shown in FIG. 10, the difference in density in the screen indicates the difference in the degree of weighting (specifically, the weighting coefficient), and the density is dark (dark). Has a lower degree of weighting than the light (bright) part.

By the way, the output for the amount of light incident on a charge storage type solid-state image sensor (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 a human perceived sensation. It is known that there is a difference in quantity. In general, the amount of light perceived by the human eye as appropriate brightness is smaller than the median value of the output obtained by linearly converting the amount of light incident on the sensor.

For example, FIG. 11 is a diagram illustrating an example of a backlit scene in which the background is high brightness with respect to a building which is the main subject. In the backlit scene illustrated in FIG. 11, when the average metering of the entire screen is simply performed, the exposure (so-called underexposure) is such that the building, which is the main subject, becomes dark due to the influence of the bright area of the sky as the background. Imaging may occur. FIG. 12 shows this state, and is a diagram illustrating a case where a building is imaged in an underexposed state in a backlit scene. As described above, the photometric result desired by the user may not be obtained due to the difference in the main subject and the change in the shooting environment.

To solve such problems, for example, the sensor output is logarithmically converted (logarithmic compression) to increase the gradation in the low-luminance region, and the gradation in the high-luminance region is compressed to compress the gradation of the human eye. A method of obtaining image data according to perception is known. For example, in Patent Document 1, the photometric values of a photometric sensor having a plurality of photometric regions are logarithmically converted, and a combined photometric output is used using a correction value according to the difference in logarithmic values between different regions (central portion and peripheral portion). There is a proposal for a technique of calculating.

Japanese Unexamined Patent Publication No. 11-38463

However, when the photometric value is logarithmically converted, the high-luminance region is compressed and output, so that when the main subject has high brightness, the gradation of the high-luminance region may deteriorate. Therefore, in the technique described in Patent Document 1, for example, when the main subject is located in the central portion of the screen and a low-luminance subject exists in the peripheral portion thereof with respect to the central portion, the main subject is appropriate based on the photometric result. There is a risk that it will not be bright. In particular, this problem becomes remarkable when the low-luminance region is wide with respect to the entire region used for photometry.

For such shooting scenes, the main subject can be made to have an appropriate brightness by using the photometric value whose sensor output is linearly transformed. However, the photometric value whose sensor output is linearly transformed can also be used. There are shooting scenes that I am not good at as mentioned above. That is, there are different cases where it is preferable to linearly transform the sensor output and when it is preferable to logarithmically transform the sensor output according to the shooting scene. An object of the present invention is to provide a photometric method capable of preventing a subject from becoming unnatural brightness regardless of a shooting scene.

In order to solve the above-mentioned problems, the image pickup apparatus of the present invention divides an imaging means that captures a subject and outputs an image and an image obtained by using the imaging means into a plurality of regions, and first A first photometric means for acquiring photometric values of the plurality of regions by a calculation method, and a second photometric means different from the first calculation method in which an image obtained by using the imaging means is divided into a plurality of regions. A second photometric means for acquiring photometric values of the plurality of regions by a calculation method, an evaluation value calculating means for calculating an evaluation value for determining exposure when imaging a subject, and the first photometric means. It has a correction value calculation means for calculating a correction value based on a difference value between a first metering result obtained by using the method and a second metering result obtained by using the second metering result. In the second calculation method, when the brightness of the subject is the same, the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. It is characterized in that the photometric values of a plurality of regions are acquired, and the evaluation value calculation means calculates the evaluation value based on the first photometric result and the correction value.

According to the present invention, it is possible to prevent the subject from becoming unnaturally bright regardless of the shooting scene.

It is a block diagram explaining the structure of the camera system 1 including the image pickup apparatus 100 which concerns on 1st Embodiment of this invention. It is a schematic block diagram of the camera system 1 including the image pickup apparatus 100 which concerns on 1st Embodiment of this invention. It is a flowchart which shows each sequence of the photometric processing which concerns on 1st Embodiment of this invention. It is a flowchart which shows each sequence of the correction value calculation process which concerns on 1st Embodiment of this invention. It is a flowchart which shows each sequence of the photometric value correction processing which concerns on 1st Embodiment of this invention. It is a figure which illustrates how the logarithmic metering value and the linear metering value change according to the difference of the luminance difference of a different area in the whole screen. It is a figure which illustrates the calculation method of the 1st correction value for the photometric value which concerns on 1st Embodiment of this invention. It is a figure which illustrates the calculation method of the attenuation coefficient γ for the photometric value correction which concerns on 1st Embodiment of this invention. It is a figure for exemplifying the subject image which concerns on the background technique of this invention. It is a figure for exemplifying the weighting table with respect to the photometric value which concerns on the background technique of this invention. It is a figure which illustrates the backlit scene which the background has high brightness with respect to the building which is the main subject which concerns on the background technique of this invention. It is a figure which illustrates the case where the building is imaged in the underexposed state in the backlight scene which concerns on the background technique of this invention. It is a figure which illustrates the shooting scene where the main subject is a high-luminance subject, and the background is low-luminance.

(First Embodiment)
(Basic configuration of camera system 1)
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a configuration of a camera system 1 including an image pickup apparatus 100 according to a first embodiment of the present invention. Further, FIG. 2 is a schematic configuration diagram of a camera system 1 including an image pickup apparatus 100 according to the first embodiment of the present invention. 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 executing software by a programmable processor (microprocessor, microcomputer) such as a CPU or MPU. It may also be realized by a combination of software and hardware. Therefore, in the following description, the same hardware can be realized as the main body even if different functional blocks are described as the main body of operation.

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

The interchangeable lens 200 is a lens unit that can be attached to and detached from the image pickup device 100, and is a lens drive that drives various lens groups 202 and apertures 204 for guiding a light beam indicating an optical image of a subject into the inside of the image pickup device 100. A unit 203 and an aperture drive unit 205 are provided. The lens control unit 201 is a control means that comprehensively controls the operation of each unit included in the interchangeable lens 200, and is connected to the overall control unit 101 of the image pickup device 100 described above to form the image pickup device 100 and the interchangeable lens 200. Various information can be exchanged between the two.

The QR mirror 102 is a quick return (QR) mirror, and the optical image of the subject incident on the inside of the image pickup device 100 is captured by the finder 123, the image sensor (image sensor B) 116 side for photometric measurement, and the image sensor (image sensor). A) An optical system for guiding to any of the 106 sides. The QR mirror 102 includes a so-called surf mirror and a sub-mirror. The optical image of the subject is guided to the image sensor 116 side for photometry and the AF sensor 121 side in the mirror down state, and the optical image of the subject is in the mirror up state. Is guided to the image sensor 106 side. The QR mirror driving unit 103 is a driving means for driving the QR mirror 102.

The pentaprism 119 is an optical system that guides the luminous flux of the subject guided by the mirror down state of the QR mirror 102 to the finder 123 and the image pickup element 116. The luminous flux guided to the image sensor 116 is guided to the image sensor 116 via the photometric optical system 122 and the bending optical system 124.

The shutter mechanism 104 is a shutter mechanism having a shutter curtain corresponding to a so-called focal plane type front curtain / rear curtain, and adjusts the exposure time and the shading state of the light incident on the image sensor A. The shutter drive unit 105 is a shutter drive means for driving the shutter mechanism 104.

The image sensor 106 (image sensor A) is an image sensor that employs a charge storage type solid-state image sensor such as CMOS that can receive the luminous flux of the subject guided by the lens group 202 and convert it into an electrical image signal. Is.

The signal processing unit 107 (signal processing unit A) is an image pickup processing means that performs various processes on the image signal output from the image pickup device 106. For example, the signal processing unit 107 performs various correction processes such as amplification processing of an image signal, A / D conversion processing for converting an analog signal into a digital signal, and scratch correction on an image signal after A / D conversion, and an image signal. Performs compression processing, etc. to compress.

The timing generation unit 108 (timing generation unit A) is a timing generation unit that outputs timing signals for adjustment when executing various operations to the image sensor 106 and the signal processing unit 107.

The recording medium IF 110 is an interface unit for recording an image signal or the like and reading an image signal or the like from the recording medium 111 with respect to the recording medium 111 that can be connected to the image pickup apparatus 100. The recording medium 111 is a recording medium made of a semiconductor memory or the like for recording various data such as an image signal, and is removable from the image pickup apparatus 100.

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

The image sensor 116 (image sensor B) is an image sensor for acquiring a light measurement signal (light measurement value) of a subject mainly used for exposure control, and like the image sensor 106, is a charge storage type solid such as CMOS. An image sensor is used. The image sensor 116 of the present embodiment includes pixels for IR (infrared) detection in addition to RGB pixels based on the so-called Bayer array. As an operation using the image sensor 116, it is possible to acquire a light source detection signal and a flicker right signal in addition to the photometry of the subject, but the description thereof will be omitted.

The signal processing unit 117 (signal processing unit B) is an image pickup processing means that performs various processes on the image signal output from the image pickup device 116. Since the content of the processing is substantially the same as that of the signal processing unit 107 described above, the description thereof will be 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 to the image sensor 116 and the signal processing unit 117. The above is the basic configuration of the camera system 1.

(Metering value correction processing)
The photometric processing according to the first embodiment of the present invention will be described with reference to FIGS. 3 to 5. FIG. 3 is a flowchart showing each sequence of photometric processing according to the first embodiment of the present invention. The photometric processing of the present embodiment includes a correction value calculation process and a photometric value correction process. Further, the photometric processing is started when the power of the image pickup device 100 is turned on, or when an image pickup instruction is given to the subject, at a periodic metering timing during so-called live view on the display device 113, but the user can arbitrarily use it. It may be configured to instruct the start at the timing.

When the photometric processing is started, as shown in FIG. 3, in step S101, the overall control unit 101 linearly converts the output of the subject image (input) incident on the image sensor 116 into a linear photometric value and logarithmic conversion (logarithmic conversion). Calculate each logarithmic photometric value (logarithmic compression). The linear metering value (linear metering value) and the logarithmic metering value (log metering value) are representative metering values of the entire screen obtained by calculation methods using different conversion characteristics. Specifically, in the present embodiment, the entire screen corresponding to the image sensor 116 is divided into a plurality of regions, the linearly converted and logarithmically converted luminance values are obtained for each pixel, and the luminance value of each pixel is obtained for each divided region. By obtaining the integral value of, the average brightness value for each divided region is obtained. Then, the summed mean value of each of the linearly transformed divided regions is taken as a linear metering value, and the summed mean value of each logarithmically transformed divided region is taken as a logarithmic metering value. In general, the logarithmic photometric value is a conversion characteristic (compression method) such that the luminance level output from the image sensor is equal to or less than the luminance level input to the image sensor with respect to the linear photometric value.

In the present embodiment, the case where the average luminance value for each divided region is added and averaged for the entire screen has been described, but the weighting degree is different for each region, and each metering is performed by the weighted average of the weighting degree and the average photometric value. It may be configured to obtain a value. Further, the unit of the luminance value and the photometric value is assumed that 1EV 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.

Next, in step S102, the overall control unit 101 executes a correction value calculation process for metering using the logarithmic metering value and the linear metering value calculated in step S101. The details of the correction value calculation process will be described later.

Next, in step S103, the overall control unit 101 executes the photometric value correction process based on the linear photometric value calculated in step S101 and the photometric correction value calculated in step S102. Details of the photometric value correction process will be described later. Then, according to the final photometric value obtained through the photometric value correction process, the exposure suitable for the photometric value is determined from the predetermined exposure conditions for exposure control, and the subject is imaged.

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

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 step S101. Specifically, in the present embodiment, the difference value is calculated by subtracting the logarithmic metering value from the linear metering value, but the absolute value of the difference between the linear metering value and the logarithmic metering value is obtained. May be good.

Here, FIG. 6 is a diagram illustrating how the logarithmic photometric value and the linear photometric value change according to the difference in the luminance difference in different regions in the entire screen. The luminance value and photometric value indicated by each line are as shown in FIG. In FIG. 6, for example, the brightness of the background (first brightness), which is the first region of the entire screen, changes, whereas the brightness of the main subject area (second brightness), which is the second region, changes. It is assumed that there is no change and it is constant. Therefore, in FIG. 6, the difference between the background brightness and the subject brightness increases toward the right side in the figure, and the difference between the two increases particularly in the region 601 shown by the broken line. In FIG. 6, one square shows a difference of about 1 EV, and the vertical axis shows the output luminance with respect to the input luminance shown by the horizontal axis.

As shown in FIG. 6, when the brightness difference in the entire screen increases due to the increase in the first brightness (background brightness), the linear photometric value increases at substantially the same rate as the first brightness, but the logarithmic photometric value is It increases at a lower rate than the first change in brightness. In other words, when the luminance shifts to the high luminance side, the larger the luminance difference in the entire screen, the larger the difference between the linear photometric value and the logarithmic photometric value. Therefore, for example, in the shooting scene shown in FIG. 11, when the exposure control based on the linear photometric value is performed, the influence of the brightness of the background is large and the building becomes dark, whereas the exposure control based on the logarithmic photometric value is used. , The influence of the brightness of the background is small and it is possible to suppress the darkening of the building. As described above, in a shooting scene in which a high-brightness subject exists, when the low-brightness subject is the main subject, the logarithmic metering value tends to make the main subject more appropriate brightness than the linear metering value.

However, even when the difference in brightness over the entire screen is large, for example, when a high-brightness subject is the main subject, the linear photometric value tends to make the main subject more appropriate than the logarithmic photometric value. .. For example, FIG. 13 is a diagram illustrating an example of a shooting scene in which the main subject is a high-brightness subject and the background is low-brightness. In the case shown in FIG. 13, based on the linear photometric value. It is easier for the main subject to have an appropriate brightness if the exposure is determined. In general, the main subject is more likely to have high brightness than low brightness. Therefore, when determining the exposure according to various shooting scenes, it tends to be more suitable for the shooting scene if the exposure is determined based on the linear photometric value, but some shooting as described above In the scene, it may be more appropriate to use logarithmic metering values.

Therefore, in the present embodiment, in order to obtain the photometric value for determining the exposure, both the linear photometric value and the logarithmic photometric value of the entire screen are calculated, and the logarithmic photometric value is taken into consideration with respect to the linear photometric value. The optimum photometric value is calculated regardless of the shooting scene. The details will be described below.

Returning to FIG. 4, in step S202, the overall control unit 101 determines whether or not the difference value obtained in step S201 is smaller than the first threshold value (threshold value 1). When it is determined that the difference value is the threshold value 1 or more (NO in step S202, the first threshold value or more), the overall control unit 101 in step S203 uses the difference value obtained in step S201 as the second threshold value (NO). It is determined whether or not the threshold value is larger than 2). Here, FIG. 7 is a diagram illustrating a method for calculating a first correction value for a photometric value according to the first embodiment of the present invention. In FIG. 7, the horizontal axis indicates the magnitude of the difference value (unit is EV), the difference is larger toward the right side, and the vertical axis indicates the degree of the first correction value (unit is EV), and the correction is made toward the lower side. The degree of is increased.

As shown in FIG. 7, when the difference value between the linear photometric value and the logarithmic photometric value is small, it is considered that the luminance difference in the entire screen is small. Therefore, in the present embodiment, when the difference value is smaller than the 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 photometric value. ..

Further, when the difference value between the linear photometric value and the logarithmic photometric value is large, it is considered that the brightness difference in the entire screen is large. Therefore, in the present embodiment, when the difference value is the threshold value 2 or more (NO in step S203), the process proceeds to step S205, and the overall control unit 101 sets the first correction value as the minimum value that can be set. Since the first correction value is a correction to the underexposed side with respect to the linear photometric value, the degree of correction is maximized when the first correction value is the minimum value.

Then, when the difference value is equal to or less than the second threshold value (the difference value is between the threshold value 1 and the threshold value 2), the overall control unit 101 sets the threshold value 1 and the threshold value 2 based on the graph shown in FIG. 7 in step S204. By linearly interpolating the corresponding first correction value, the first correction value corresponding to the difference value is obtained. The table data of the first correction value corresponding to the difference value may be stored in the memory unit 109 in advance, and the first correction value may be calculated based on the table data.

After calculating the first correction value by the method described above, in steps S207 to S211, the attenuation coefficient γ to be multiplied by the first correction value is calculated. FIG. 8 is a diagram illustrating a method for calculating an attenuation coefficient γ for photometric value correction according to the first embodiment of the present invention. In FIG. 8, the horizontal axis indicates the magnitude of the linear photometric value (unit: EV), the brightness becomes higher toward the right side, and the vertical axis indicates the ratio of the attenuation coefficient γ.

As described above, the first correction value has a configuration in which the degree of correction increases as the difference value between the linear metering value and the logarithmic metering value increases. Therefore, when the main subject is a low-brightness subject, the main subject The brightness can be brought close to appropriate. However, in a scene where the screen is dark as a whole, if the linear photometric value is corrected based on the first correction value, the main subject may become dark. For example, it is assumed that the background is dark due to a subject exposed to a spotlight, or a point light source such as an electric lamp exists in the screen when shooting outdoors at night. In such a case, the linear photometric value is high because there is a high-luminance region in the screen, but the logarithmic photometric value tends to be low because there are many appropriate regions occupying the entire screen, so the difference in brightness between the two is large. Become. Then, in such a case, if the linear photometric value is corrected based on the first correction value, for example, the main subject in the high-luminance region becomes dark when shooting a spotlight, and the actual subject is darkened when shooting at night. An image that is unnaturally bright with respect to the ambient illuminance is acquired.

Therefore, in the present embodiment, a configuration is adopted in which the linear photometric value is corrected based on the second correction value β obtained by multiplying the first correction value by the attenuation coefficient γ. Then, the attenuation coefficient γ is reduced as the linear photometric value is smaller (that is, the entire image is darker) so that the degree of correction of the second correction value after multiplying the attenuation coefficient γ is reduced. The formula (1) shown below is a formula for calculating the second correction value β described later, and in the formula, the above-mentioned first correction value is α.
Second correction value β = γ × first correction value α ... (1)

According to the equation (1), for example, when the attenuation coefficient γ is 0, the second correction value β is also 0, and the linear photometric value does not change (does not correct) before and after the correction. On the other hand, according to the equation (1), as the attenuation coefficient increases, the degree of correction of the second correction amount β increases.

Therefore, in the present embodiment, even if the brightness difference of the entire screen is large and the degree of the first correction value is maximized, the photometric value becomes unnecessarily dark in a scene where the entire screen is dark. It is possible to suppress the correction to. According to the present embodiment, it is possible to effectively suppress underexposure of the subject in a scene in which the brightness difference of the entire screen is large and the entire screen is not dark.

Returning to FIG. 4, in step S207, the overall control unit 101 determines whether or not the linear photometric value obtained in step S101 is smaller than the third threshold value (threshold value 3). When it is determined that the linear photometric value is smaller than the threshold value 3 (YES in step S207), the attenuation coefficient γ with respect to the first correction value is set to 0.

When it is determined that the linear photometric value is the threshold value 3 or more (NO in step S207), the overall control unit 101 in step S208 has the linear photometric value obtained in step S101 larger than the fourth threshold value (threshold value 4). Judge whether or not. Then, when it is determined that the linear photometric value is the threshold value 4 or more (YES in step S208), the attenuation coefficient γ with respect to the first correction value is set to 1.

When the linear metering value is located between the threshold value 3 and the threshold value 4, in step S209, the overall control unit 101 linearly interpolates the attenuation coefficient γ corresponding to the threshold value 3 and the threshold value 4 based on the graph shown in FIG. Then, the attenuation coefficient γ corresponding to the linear metering value is obtained. The table data of the attenuation coefficient γ corresponding to the linear photometric value may be stored in the memory unit 109 in advance, and the attenuation coefficient γ may be calculated based on the table data.

Finally, in S212, the overall control unit 101 has a second correction value from the 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. Calculate β. The above is the correction value calculation process according to the present embodiment. The process of steps S207 to S211 is a process of improving the accuracy of correcting the linear photometric value in the optimum shooting scene, and may be configured not to execute the process of steps S207 to S211. In this case, in terms of the control algorithm of the image pickup apparatus 100, the second correction value may be controlled to be the same as the first correction value. When this configuration is adopted, a high-brightness subject may be underexposed, but if the degree of the problem and the frequency of the problem occur are low, the first correction value is calculated without performing the processes of steps S207 to S211. It is effective enough to solve the problem of the present invention.

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

First, in step S301, the overall control unit 101 determines whether or not the selection method (mode) of the distance measurement point (distance measurement area) currently set in the image pickup apparatus 100 is the automatic selection method. If it is determined that the AF point selection method is the automatic selection method (YES in step S301), the process proceeds to step S302, and if it is not determined (NO in step S301), the process proceeds to step S305.

In step S305, the overall control unit 101 determines that the photometric value is not corrected, and sets the above-mentioned second correction value so as not to be corrected with respect to the linear photometric value. For example, when the user manually sets the photometric point selection method (that is, the photometric point), the photometric value may be determined according to the photometric point selected by the user's manual operation. In this case, if the image pickup apparatus 100 automatically corrects the linear photometric value, there is a risk that a photometric result unintended by the user may be obtained. Therefore, according to the determination in step S301, if the selection method of the focusing point is not automatic selection, the linear metering value is controlled so as not to be corrected, thereby suppressing the unintended photometric result of the user. it can.

Next, in step S302, the overall control unit 101 determines whether or not the subject distance to the main subject is equal to or greater than a predetermined value. If it is determined by the determination in step S302 that the subject distance to the main subject is equal to or less than the predetermined value, the process proceeds to step S304, and if it is determined that the subject distance to the main subject is larger than the predetermined value, the process proceeds to step S303. move on.

Generally, when the distance to the subject is short, the area ratio occupied by the subject to the entire screen also increases. In this case, since a linear photometric value corresponding to the subject having a high occupancy rate with respect to the entire screen can be obtained, it is less necessary to correct the photometric value. In step 302, this point can be determined to prevent the photometric value from being unnaturally corrected for a subject having a high occupancy with respect to the entire screen.

As the method for detecting the main subject in step S302, any known method may be adopted. For example, the subject may be detected by using subject detection technology such as pattern matching or contrast matching, or in addition to this, a configuration in which a subject that occupies a large proportion of the entire screen is the main subject may be adopted. Just do it.

Further, in the process of step S302, the distance to the main subject is determined, but the present invention is not limited to this. For example, as the process of step S302, a determination method for comparing the shooting magnification with a predetermined value may be used, or a method for determining the ratio of the subject to the entire screen may be used.

Next, in step S303, the overall control unit 101 determines whether or not a face region exists in the screen. If it is determined in step S303 that the face area exists, the process proceeds to step S305, and if it is determined that the face area does not exist, the process proceeds to step S304. When a face area exists in the screen, it is highly possible that an image having the brightness intended by the user is acquired by calculating the photometric value according to the face area. Therefore, according to the determination in step S303, when the face region exists in the screen, the linear photometric value is controlled so as not to be corrected, and the acquisition of an image having an unintended brightness by the user is effectively suppressed. To do.

As the method for detecting the face region in step S303, any known method may be adopted. Further, the order of processing in steps S302 and S303 is not limited to the order described above, and for example, the processing in step S303 may be executed first. Further, since the photometric value correction process executed in the present embodiment is a process for determining the condition under which the photometric value can be effectively corrected by the second correction value calculated in the correction value calculation process, the photometric value correction is performed. The configuration may not execute the process itself. When the photometric value correction process is executed, the probability of obtaining an image with the brightness intended by the user is higher than when the photometric value correction process is not executed.

When the process proceeds to step S304 based on the determination results of steps S301 to S303 described above, the overall control unit 101 executes correction for the linear photometric value based on the above-mentioned second correction value, and finally photometric measurement is performed. Calculate the value. That is, the overall control unit 101 (evaluation value calculation means) calculates the final photometric value as an evaluation value for determining the exposure when the subject is imaged and the image is acquired. When the process proceeds to step S305, the linear photometric value is not corrected as described above, so the linear photometric value calculated in step S101 is used as the final photometric value.

The above is the photometric value correction process according to the present embodiment. After the photometric value correction process is completed, the exposure is determined based on the acquired final photometric value (final photometric value), and the subject is imaged based on the exposure, so that the subject is not affected by the shooting scene. It is possible to obtain an image with a brightness suitable for the above.

In addition, as the order of the processes of steps S102 and S103 in FIG. 3 described above, the process of step S103 may be executed first. In this case, the photometric value calculation process may be executed only when the process of step S304 is performed in the photometric value correction process to calculate the final photometric value. In other words, if the process of step S305 is performed in the photometric value correction process, the final photometric value may be determined without executing the photometric value calculation process. In this case, unnecessary correction value calculation process is performed. Therefore, the processing load of the image pickup apparatus 100 can be reduced.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and modifications can be made within the scope of the gist thereof. For example, in the above-described embodiment, the image pickup device including the optical lens integrally has been described, but a so-called interchangeable lens type image pickup device may be adopted.

Further, in the above-described embodiment, the application of the correction value to the linear photometric value has been mentioned, but the present invention is not limited to this, and the correction value may be applied to the logarithmic photometric value. For example, a backlight scene is illustrated as a shooting scene that needs to be corrected for a linear photometric value, but as a shooting scene that needs to be corrected for a logarithmic photometric value, the main subject is high, as in the spotlight shooting described above. This corresponds to the case where the background is low brightness with brightness.

In the case of spotlight photography, if the exposure is determined based on the logarithmic photometric value, the main subject to which the spotlight is applied may be overexposed and saturated due to the influence of the low brightness region of the background.

Therefore, in the configuration in which the exposure is determined based on the logarithmic metering value, as described above, the difference value of both the logarithmic metering value and the linear metering value is obtained, and the logarithm is obtained according to the magnitude of the difference value and the logarithmic metering value. A configuration that corrects the photometric value may be adopted. Specifically, the first correction value α described above with reference to FIG. 7 is determined based on table data such that plus and minus are reversed from those of the first embodiment described above. In this case, as the difference value becomes larger, 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.

Further, the attenuation coefficient γ may be determined so that the attenuation rate with respect to the first correction value becomes higher (the degree of correction becomes smaller) when the logarithmic photometric value is bright. For example, the attenuation coefficient γ may be the threshold value shown in FIG. The determination may be made based on table data in which the relationship between the attenuation coefficients is reversed.

In the above-described embodiment, the linear photometric value and the logarithmic photometric value are mentioned as the photometric values to be calculated, but the embodiment of the present invention is based on two methods in which the characteristics of the output with respect to the input to the image sensor are different. It is applicable if it is configured to acquire separate photometric values. For example, the present invention can be applied as long as the input / output characteristic is a configuration in which a photometric value having a different slope of the conversion characteristic with respect to the conversion characteristic is obtained based on a linear conversion in which the output is 1: 1 with respect to the input. In this case, the direction of the correction value with respect to the difference value (absolute value may be sufficient) depending on whether the conversion characteristic is steep or gentle with respect to the photometric value obtained based on the conversion characteristic of the correction target. The sex (underexposed side or overexposed side) changes.

Further, in the above-described embodiment, the configuration for calculating the photometric value using the image sensor 116 has been described, but it can also be applied to the case where the photometric value is calculated using the image sensor 106. That is, the present invention can be applied even in a configuration having only an image pickup device that acquires an image signal for recording.

In the above-described embodiment, a digital camera has been described as an example of the image pickup apparatus for carrying out the present invention, but the present invention is not limited thereto. For example, a configuration may employ 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.

1 Camera system 100 Image pickup device 101 Overall control unit 106 Image pickup element A
116 Image sensor B
200 interchangeable lens

Claims (14)

An imaging means that captures a subject and outputs an image,
A first photometric means that divides an image obtained by using the imaging means into a plurality of regions and acquires photometric values of the plurality of regions by a first calculation method.
A second photometric means that divides an image obtained by using the imaging means into a plurality of regions and acquires photometric values of the plurality of regions by a second calculation method different from the first calculation method.
Evaluation value calculation means for calculating the evaluation value for determining the exposure when imaging the 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. When,
Have,
In the second calculation method, when the brightness of the subject is the same, the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. Obtain the photometric values of the plurality of regions and obtain
The evaluation value calculation means is an imaging device characterized in that the evaluation value is calculated based on the first photometric result and the correction value. The correction value calculating means is such that the first correction value is larger when the difference value is equal to or greater than the first threshold value than when the difference value is smaller than the first threshold value. The imaging device according to claim 1, wherein the imaging device performs an operation. The correction value calculating means said that when the difference value is larger than the second threshold value which is larger than the first threshold value, it is larger than when the difference value is equal to or less than the second threshold value. The imaging apparatus according to claim 2, wherein the calculation is performed so that the correction value of is large. In the correction value calculating means, when the difference value is equal to or more than the first threshold value and equal to or less than the second threshold value, the first correction value is smaller than the first threshold value. The calculation is performed so that the value is between the first correction value set in the case and the first correction value set when the difference value is larger than the second threshold value. The imaging apparatus according to claim 3. The correction value calculation means calculates the second correction value by multiplying the first correction value based on the difference value by the attenuation coefficient according to the first photometric result.
The imaging device according to any one of claims 1 to 4, wherein the evaluation value calculating means calculates the evaluation value based on the first photometric result and the second correction value. The first photometric result and the second photometric result have a photometric value indicated by the brightness value of the subject, and the correction value calculating means obtains the attenuation coefficient as the first photometric result is smaller. The imaging according to claim 5, wherein the attenuation coefficient is set to approach 1 as the first photometric result approaches 0 and the larger the photometric value is, and the second correction value is calculated. apparatus. The evaluation value calculating means is characterized in that when a method of selecting a ranging region by a manual operation of a user is set 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. A claim characterized in that the evaluation value calculating means calculates the evaluation value based on the first photometric result and the correction value when the area of the main subject occupying the entire screen is larger than a predetermined value. Item 2. The imaging apparatus according to any one of Items 1 to 7. The imaging device according to any one of claims 1 to 8, wherein the evaluation value calculating means calculates the evaluation value regardless of the correction value when the entire screen includes a face region. .. In the second calculation method, when the brightness of the subject is the same, the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. The imaging apparatus according to any one of claims 1 to 9, wherein the photometric values of the plurality of regions are acquired based on a conversion characteristic that logarithmically compresses the photometric values. An imaging means that captures a subject and outputs an image,
A first photometric means that divides an image obtained by using the imaging means into a plurality of regions and acquires photometric values of the plurality of regions by a first calculation method.
A second photometric means that divides an image obtained by using the imaging means into a plurality of regions and acquires photometric values of the plurality of regions by a second calculation method different from the first calculation method.
Evaluation value calculation means for calculating the evaluation value for determining the exposure when imaging the 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. When,
Have,
In the second calculation method, when the brightness of the subject is the same, the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. Obtain the photometric values of the plurality of regions and obtain
The evaluation value calculating means is an imaging device characterized in that the evaluation value is calculated based on the second photometric result and the correction value. It is a control method of an imaging device provided with an imaging means that captures an image of a subject and outputs an image.
A first photometric step of dividing an image obtained by using the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions by a first calculation method.
A second photometric step of dividing an image obtained by using the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions by a second calculation method different from the first calculation method.
The evaluation value calculation process for calculating the evaluation value for determining the exposure when imaging the subject, and the evaluation value calculation process.
A correction value calculation step of calculating a correction value based on a difference value between the first photometric result obtained in the first photometric step and the second photometric result obtained in the second photometric step.
Have,
In the second calculation method, when the brightness of the subject is the same, the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. Obtain the photometric values of the plurality of regions and obtain
The evaluation value calculation step is a control method for an imaging device, characterized in that the evaluation value is calculated based on the first photometric result and the correction value. It is a control method of an imaging device provided with an imaging means that captures an image of a subject and outputs an image.
A first photometric step of dividing an image obtained by using the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions by a first calculation method.
A second photometric step of dividing an image obtained by using the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions by a second calculation method different from the first calculation method.
The evaluation value calculation process for calculating the evaluation value for determining the exposure when imaging the subject, and the evaluation value calculation process.
A correction value calculation step of calculating a correction value based on a difference value between the first photometric result obtained in the first photometric step and the second photometric result obtained in the second photometric step.
Have,
In the second calculation method, when the brightness of the subject is the same, the brightness level output from the imaging means is lower than the brightness level input to the imaging means as compared with the first calculation method. Obtain the photometric values of the plurality of regions and obtain
The evaluation value calculation step is a control method for an imaging device, characterized in that the evaluation value is calculated based on the second photometric result and the correction value. A computer-readable program for causing a computer to execute the control method of the imaging device according to claim 12 or 13.

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