JP7682954B2 - Imaging device, control method and program thereof - Google Patents

Description

The present invention relates to an imaging device, its control method and program, and in particular to a method for measuring the light of a subject.

Conventionally, a method for setting exposure when capturing an image of a subject based on a photometric value obtained by measuring the photometric value of the subject is known. For example, FIG. 9 is a diagram for illustratively explaining a certain subject image. In the example shown 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. For example, FIG. 10 is a diagram for illustratively explaining a weighting table for photometric values. As shown in FIG. 10, the photometric value of the entire screen can be obtained by multiplying the photometric values obtained in each area by an arbitrary weighting table and performing a weighted average. In the exemplary photometric weighting table shown in FIG. 10, the difference in density within the screen indicates the difference in the weighting degree (specifically, the weighting coefficient), and the weighting degree is lower for darker (darker) areas than for lighter (brighter) areas.

The output of a charge-storage solid-state imaging device (sensor) such as a CCD or CMOS sensor in response to the amount of light incident on that sensor is a physical signal amount that is linear with respect to the input, but it is known that there are differences in the sensory amount that humans perceive. In general, the amount of light that the human eye perceives 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 highly luminous compared to the main subject, a building. In the backlit scene shown in FIG. 11, if average metering of the entire screen is simply performed, there is a risk that the image will be captured with an exposure that makes the main subject, the building, dark (so-called underexposure) due to the influence of bright areas of the sky in the background. FIG. 12 shows this state, and is a diagram illustrating an example of a case in which a building is captured in an underexposed state in a backlit scene. In this way, differences in the main subject and changes in the shooting environment may prevent the user from obtaining the metering results that they desire.

To address this issue, a method is known in which the sensor output is logarithmically converted (logarithmic compression) to increase the gradation in low-luminance areas and compress the gradation in high-luminance areas, thereby obtaining image data that matches the perception of the human eye. For example, Patent Document 1 proposes a technique in which the photometric value of a photometric sensor having multiple photometric areas is logarithmically converted, and a composite photometric output is calculated using a correction value according to the difference in logarithmic values between different areas (the center and its periphery).

Japanese Patent Application Publication No. 11-38463

However, when the photometric value is logarithmically converted, the high-brightness areas are compressed before being output, and so there is a risk that the gradation of the high-brightness areas will decrease if the main subject is highly bright. Therefore, with the technology described in Patent Document 1, for example, if the main subject is located in the center of the screen and there is a low-brightness subject on the periphery of the center, there is a risk that the main subject will not be properly illuminated as a result of the photometry. This problem is particularly noticeable when the low-brightness areas are wide compared to the total area used for photometry.

For such shooting scenes, the main subject can be appropriately brightened by using a photometric value obtained by linearly converting the sensor output, but as mentioned above, there are shooting scenes in which the photometric value obtained by linearly converting the sensor output is not suitable. In other words, depending on the shooting scene, there are different 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 that can prevent the subject from appearing unnaturally bright, regardless of the shooting scene.

In order to solve the above problems, the imaging device of the present invention has an imaging means for imaging a subject and outputting the image, a first photometry means for dividing an image obtained using the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions using a first calculation method, a second photometry means for dividing an image obtained using the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions using a second calculation method different from the first calculation method, an evaluation value calculation means for calculating an evaluation value for determining exposure when imaging the subject, and a correction value calculation means for calculating a correction value based on a difference value between the first photometry result obtained using the first photometry means and the second photometry result obtained using the second photometry result, and the second photometry means acquires a photometry value for the plurality of regions that is equal to or less than the photometry value acquired by the first photometry means when the luminance of the subject is the same, and the evaluation value calculation means calculates the evaluation value based on the first photometry result and the correction value.

The present invention makes it possible to prevent the subject from appearing unnaturally bright, regardless of the shooting scene.

1 is a block diagram illustrating a configuration of a camera system 1 including an imaging device 100 according to a first embodiment of the present invention. 1 is a schematic configuration diagram of a camera system 1 including an imaging device 100 according to a first embodiment of the present invention. 5 is a flowchart showing each sequence of a photometry process according to the first embodiment of the present invention. 5 is a flowchart showing each sequence of a correction value calculation process according to the first embodiment of the present invention. 5 is a flowchart showing the sequence of a photometric value correction process according to the first embodiment of the present invention. 10A and 10B are diagrams illustrating an example of how logarithmic photometric values and linear photometric values change in response to differences in luminance differences between different regions across the entire screen. 5A to 5C are diagrams illustrating an example of a method for calculating a first correction value for a photometric value according to the first embodiment of the present invention. 5A to 5C are diagrams illustrating an example of a method for calculating an attenuation coefficient γ for photometric value correction according to the first embodiment of the present invention. 1A to 1C are diagrams for explaining an example of a subject image according to the background art of the present invention; FIG. 1 is a diagram for explaining an example of a weighting table for photometric values according to the background art of the present invention; 1 is a diagram for explaining an example of a backlit scene in which the background has high luminance against a building that is a main subject according to the background art of the present invention; FIG. 1 is a diagram for explaining an example of a case where a building is imaged in an underexposed state in a backlit scene according to the background art of the present invention. 1 is a diagram for explaining an example of a photographing scene in which a main subject is a high-luminance subject and the background is low-luminance;

First Embodiment
(Basic configuration of camera system 1)
A preferred embodiment of the present invention will be described below with reference to 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. FIG. 2 is a schematic configuration diagram of a camera system 1 including an imaging device 100 according to a first embodiment of the present invention. Note that one or more of the functional blocks shown in FIG. 1 and FIG. 2 may be realized by hardware such as an ASIC or a programmable logic array (PLA). Also, they may be realized by a programmable processor (microprocessor, microcomputer) such as a CPU or MPU executing software. Also, they may be realized by a combination of software and hardware. Therefore, even if different functional blocks are described as operating subjects in the following description, the same hardware may be realized as the subject.

The overall control unit 101 is made up of a calculation device such as a CPU (Central Processing Unit), is connected to each block described below, and is a control means capable of overall control of the image capture device 100 and each unit attached to the image capture 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 in which programs for operating the overall control unit 101 and various adjustment parameters are recorded. Programs read from this ROM area are expanded and executed in the RAM area, which is a volatile recording element. The RAM area is a so-called frame memory, and is a storage unit that temporarily stores image signals and can be read out when necessary.

The interchangeable lens 200 is a lens unit that can be attached to and detached from the imaging device 100, and includes various lenses 202 and an aperture 204 for directing a light beam representing an optical image of a subject into the imaging device 100, as well as a lens driver 203 and an aperture driver 205 for driving these. The lens control unit 201 is a control means that comprehensively controls the operation of each unit included in the interchangeable lens 200, and by connecting to the overall control unit 101 of the imaging device 100 described above, various information can be exchanged between the imaging device 100 and the interchangeable lens 200.

The QR mirror 102 is a quick return (QR) mirror, and is an optical system for directing the optical image of the subject that enters the inside of the imaging device 100 to either the viewfinder 123 and the photometry imaging element (image element B) 116 side or the image element (image element A) 106 side. The QR mirror 102 is equipped with a so-called surf mirror and a sub-mirror, and in the mirror down state, the optical image of the subject is directed to the photometry imaging element 116 side and the AF sensor 121 side, and in the mirror up state, the optical image of the subject is directed to the image element 106 side. The QR mirror driver 103 is a driving means for driving the QR mirror 102.

The pentaprism 119 is an optical system that guides the subject light beam guided to the QR mirror 102 in the mirror-down state to the viewfinder 123 and the image sensor 116. The light beam guided to the image sensor 116 is guided to the image sensor 116 via the photometry optical system 122 and the bending optical system 124.

The shutter mechanism 104 is a shutter mechanism having shutter curtains equivalent to the front and rear curtains of a so-called focal plane type, and adjusts the exposure time and light blocking state of light incident on the image sensor A. The shutter drive unit 105 is a shutter drive means that drives the shutter mechanism 104.

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

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 performs amplification processing of the image signal, A/D conversion processing for converting an analog signal to 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.

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

The recording medium IF 110 is an interface unit for recording image signals and the like to a recording medium 111 that can be connected to the imaging device 100, and for reading image signals and the like from the recording medium 111. The recording medium 111 is a recording medium made of a semiconductor memory or the like that records various data such as image signals, and is detachable from the imaging device 100.

The display drive unit 112 is a display drive means that drives the display device 113, which converts image signals obtained by capturing an image of a subject into display signals and displays them. The external IF 114 is an external interface unit that controls the transmission and reception of information such as image signals and control signals to and from external devices such as a computer 115.

The image sensor 116 (image sensor B) is an image sensor for acquiring a photometric signal (photometric value) of a subject that is mainly used for exposure control, and like the image sensor 106, employs a charge-storage type solid-state image sensor such as a CMOS. Note that the image sensor 116 of this embodiment is equipped with pixels for IR (infrared) detection in addition to RGB pixels based on a so-called Bayer array. Operations using the image sensor 116 include acquiring a light source detection signal and a flicker right signal in addition to photometry of the subject, but a description thereof will be omitted.

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. The content of the processing is substantially the same as that of the signal processing unit 107 described above, so a description thereof will be omitted. In addition, the timing generating unit 118 (timing generating unit B) is a timing generating means that outputs timing signals for adjustment when performing various operations to the imaging element 116 and the signal processing unit 117. The above is the basic configuration of the camera system 1.

(Photometric value correction process)
The photometry process according to the first embodiment of the present invention will be described with reference to Fig. 3 to Fig. 5. Fig. 3 is a flowchart showing the sequences of the photometry process according to the first embodiment of the present invention. The photometry process according to this embodiment includes a correction value calculation process and a photometry value correction process. The photometry process is started when the power supply of the image capture device 100 is turned on, when an instruction to capture an image of a subject is given, or at regular photometry timing during a so-called live view on the display device 113, but may be started at any timing by the user.

When the photometry 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 for the subject image (input) incident on the image sensor 116, and a logarithmic photometric value obtained by logarithmically converting (logarithmic compression). 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 this embodiment, the entire screen corresponding to the image sensor 116 is divided into multiple regions, and linearly and logarithmically converted luminance values are obtained for each pixel, and the average luminance value for each divided region is obtained by calculating the integral value of the luminance value of each pixel for each divided region. The linearly converted average value of each divided region is then set as the linear photometric value, and the logarithmic converted average value of each divided region is set as the logarithmic photometric 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 lower than the luminance level input to the image sensor for the linear photometric value.

In this embodiment, the average brightness value for each divided region is calculated for the entire screen, but the weighting degree may be different for each region, and each photometric value may be calculated by the weighted average of the weighting degree and the average photometric value. The units of brightness value and photometric value are based on the logarithmic converted state, with 1 EV in the so-called APEX (Additive System of Photographic Exposure) system corresponding to one step of brightness value and photometric value.

Next, in step S102, the overall control unit 101 executes a process for calculating a correction value for photometry using the logarithmic photometric value and the linear photometric 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 a photometric value correction process based on the linear photometric value calculated in step S101 and the photometric correction value calculated in step S102. The photometric value correction process will be described in detail later. Then, in accordance with the final photometric value obtained through the photometric value correction process, an exposure appropriate for the photometric value is determined from predetermined exposure conditions for exposure control, and an image of the subject is captured.

Figure 4 is a flowchart showing each sequence of the correction value calculation process according to the first embodiment of the present invention, which corresponds to step S102 in the photometry process described above. The correction value calculation process according to this embodiment will be described below with reference to Figures 4 and 6 to 8.

When the correction value calculation process is started, first, in step S201, the overall control unit 101 calculates the difference 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 the absolute value of the difference between the linear photometric value and the logarithmic photometric value may be calculated.

Here, FIG. 6 is a diagram for explaining an example of how logarithmic photometric values and linear photometric values change according to the difference in luminance difference between different areas on the entire screen. The luminance values and photometric values indicated by each line are as shown in FIG. 6. In FIG. 6, for example, it is assumed that the luminance (first luminance) of the background, which is the first area on the entire screen, changes, while the luminance (second luminance) of the main subject area, which is the second area, remains constant. Therefore, in FIG. 6, the difference between the background luminance and the subject luminance increases toward the right side of the figure, and the difference between the two is particularly large in the area 601 indicated by the dashed line. Note that in FIG. 6, one square indicates a difference of approximately 1 EV, and the vertical axis indicates the output luminance while the horizontal axis indicates the input luminance.

As shown in FIG. 6, when the luminance difference in the entire screen increases due to an increase in the first luminance (background luminance), the linear photometric value increases at approximately the same rate as the first luminance, but the logarithmic photometric 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 in the entire screen, the greater the difference between the linear photometric value and the logarithmic photometric value. Therefore, for example, in a shooting scene such as that shown in FIG. 11, when 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 exposure control based on the logarithmic photometric value is small and the influence of the brightness of the background is small, and the building can be prevented from becoming dark. Thus, in a shooting scene in which a high-luminance subject exists, when a low-luminance subject is the main subject, the main subject is more likely to be appropriately bright with the logarithmic photometric value than with the linear photometric value.

However, even when the brightness difference across the entire screen is large, for example, when the main subject is a high-brightness subject, linear photometry is more likely to give the main subject the appropriate brightness than logarithmic photometry. 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 a case such as that shown in FIG. 13, determining the exposure based on linear photometry is more likely to give the main subject the appropriate brightness. In general, the main subject is more likely to be high-brightness than low-brightness. Therefore, when determining the exposure for various shooting scenes, determining the exposure based on linear photometry tends to give the brightness appropriate for the shooting scene, but in some shooting scenes such as those described above, using logarithmic photometry may be more appropriate.

Therefore, in this embodiment, to obtain the photometric value for determining the exposure, both the linear photometric value and the logarithmic photometric value for the entire screen are calculated, and the linear photometric value is corrected taking into account the logarithmic photometric value, thereby calculating the optimal photometric value regardless of the shooting scene. The details of this are explained below.

Returning to FIG. 4, in step S202, the overall control unit 101 determines whether the difference value obtained in step S201 is smaller than the first threshold value (threshold 1). If it is determined that the difference value is equal to or greater than 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 the second threshold value (threshold 2). Here, FIG. 7 is a diagram illustrating an example of 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: EV), with the difference increasing toward the right, and the vertical axis indicates the degree of the first correction value (unit: EV), with the degree of correction increasing toward the bottom.

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

In addition, when the difference between the linear photometry value and the logarithmic photometry value is large, it is considered that the brightness difference across the entire screen is large. Therefore, in this embodiment, when the difference is equal to or greater than threshold value 2 (NO in step S203), the process proceeds to step S205, where the overall control unit 101 sets the first correction value to the minimum value that can be set. Note that since the first correction value is a correction toward the underexposure side with respect to the linear photometry value, the degree of correction is maximum when the first correction value is the minimum value.

If 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 find the first correction value corresponding to the difference value. Note that table data of the first correction values 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.

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 an example of a method for calculating the 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), with the brightness increasing as one moves to the right, and the vertical axis indicates the proportion of the attenuation coefficient γ.

As described above, the first correction value is configured such that the degree of correction increases as the difference between the linear photometry value and the logarithmic photometry value increases, so that when the main subject is a low-luminance subject, the brightness of the main subject can be brought closer to the appropriate level. However, in a scene where the screen is dark overall, correcting the linear photometry value based on the first correction value may cause the main subject to become dark. For example, a subject may be illuminated by a spotlight and have a dark background, or a point light source such as an electric lamp may be present in the screen when shooting outdoors at night. In such a case, the linear photometry value is high because there is a high-luminance area in the screen, but the logarithmic photometry value tends to be low because there is a large amount of moderate area occupying the entire screen, so the brightness difference between the two is large. In such a case, if the linear photometry value is corrected based on the first correction value, for example, when shooting a spotlight, the main subject in the high-luminance area becomes dark, and when shooting at night, an image that is unnaturally bright compared to the actual environmental illuminance is obtained.

Therefore, in this embodiment, a configuration is adopted in which the linear photometric value is corrected based on a second correction value β obtained by multiplying the first correction value by an attenuation coefficient γ. The attenuation coefficient γ is made smaller the smaller the linear photometric value (i.e., the darker the entire image), so that the degree of correction of the second correction value after multiplication 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 photometric value does not change before and after correction (no correction is performed). On the other hand, according to formula (1), the degree of correction of the second correction amount β increases as the attenuation coefficient increases.

Therefore, in this embodiment, even if the brightness difference across the screen is large and the degree of the first correction value is maximized, in a scene where the entire screen is dark, it is possible to prevent the photometric value from being corrected to be unnecessarily dark. According to this embodiment, in a scene where the brightness difference across the screen is large and the entire screen is not dark, it is possible to effectively prevent the subject from being underexposed.

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

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

If the linear photometric value is between threshold value 3 and threshold value 4, in step S209, the overall control unit 101 linearly interpolates the attenuation coefficient γ corresponding to threshold value 3 and threshold value 4 based on the graph shown in Fig. 8 to find the attenuation coefficient γ corresponding to the linear photometric value. Note that the configuration may be such that table data of the attenuation coefficient γ corresponding to the linear photometric value is stored in advance in the memory unit 109, and the attenuation coefficient γ is calculated based on the table data.

Finally, in S212, the overall control unit 101 calculates the second correction value β from equation (1) based on the first correction value α calculated in steps S204 to S206 and the attenuation coefficient γ calculated in steps S209 to S211. The above is the correction value calculation process according to this embodiment. Note that the processes in steps S207 to S211 are processes for improving the accuracy of correcting the linear photometric value in the optimal shooting scene, and the configuration may be such that the processes in steps S207 to S211 are not executed. In this case, the control algorithm of the imaging device 100 only needs to control the second correction value to be the same as the first correction value. When this configuration is adopted, there is a possibility that a high-luminance subject will be underexposed, but if the degree of the problem and the frequency with which the problem occurs 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.

Next, the photometric value correction process according to this embodiment will be described with reference to FIG. 5. FIG. 5 is a flowchart showing the sequences of the photometric value correction process according to the first embodiment of the present invention, which corresponds to step S103 in the photometric process described above.

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

In step S305, the overall control unit 101 determines that the photometry value is not to be corrected, and sets the second correction value described above so as not to correct the linear photometry value. For example, if the user manually sets the range-finding point selection method (i.e., the range-finding point), the photometry value can be determined according to the range-finding point selected by the user's manual operation. In this case, if the imaging device 100 automatically corrects the linear photometry value, there is a risk that a photometry result unintended by the user will be obtained. Therefore, by controlling not to correct the linear photometry value if the range-finding point selection method is not automatically selected as determined in step S301, it is possible to prevent a photometry result unintended by the user.

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 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 greater than the predetermined value, the process proceeds to step S303.

Generally, when the distance to the subject is short, the area ratio of the subject to the entire screen is also large. In this case, a linear photometric value corresponding to the subject that occupies a large proportion of the entire screen is obtained, so there is little need to correct the photometric value. In step 302, this point is determined, and unnatural correction of the photometric value for a subject that occupies a large proportion of the entire screen can be suppressed.

The method for detecting the main subject in step S302 may be any known method. For example, a subject may be detected using a subject detection technique such as pattern matching or contrast matching, or a subject that occupies a large proportion of the entire screen may be treated as the main subject.

In addition, the process of step S302 is configured to determine the distance to the main subject, but this is not limited to this. For example, the process of step S302 may be a determination method in which the shooting magnification is compared with a predetermined value, or a method in which the proportion of the subject that occupies the entire screen may be determined.

Next, in step S303, the overall control unit 101 determines whether or not a face area is present on the screen. If it is determined in step S303 that a face area is present, the process proceeds to step S305, and if it is determined that a face area is not present, the process proceeds to step S304. If a face area is present on the screen, calculating a photometric value according to the face area increases the likelihood that an image with the brightness intended by the user will be captured. Therefore, if it is determined in step S303 that a face area is present on the screen, control is performed so that no correction is made to the linear photometric value, effectively preventing an image with a brightness unintended by the user from being captured.

The method for detecting the face area in step S303 may be any known method. The order of steps S302 and S303 is not limited to the above-mentioned order, and for example, the process of step S303 may be performed first. Furthermore, since the photometric value correction process performed in this embodiment is a process for determining the conditions under which the photometric value can be effectively corrected using the second correction value calculated in the correction value calculation process, the configuration may not require the photometric value correction process to be performed. The probability of obtaining an image with the brightness intended by the user is higher when the photometric value correction process is performed than when it is not performed.

If the process proceeds to step S304 based on the judgment results of steps S301 to S303 described above, the overall control unit 101 performs correction on the linear photometric value based on the second correction value described above, and calculates the final photometric value. In other words, the overall control unit 101 (evaluation value calculation means) calculates the final photometric value as an evaluation value for determining the exposure when capturing an image of a subject. Note that if the process proceeds to step S305, the linear photometric value is not corrected as described above, and the linear photometric value calculated in step S101 is used as the final photometric value.

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 acquired final photometry value (final photometry value), and an image of the subject is captured based on that exposure, making it possible to obtain an image with a brightness appropriate for the subject regardless of the shooting scene.

The order of steps S102 and S103 in FIG. 3 described above may be such that step S103 is executed first. In this case, the photometric value calculation process is executed only when the photometric value correction process proceeds to step S304, and the final photometric value is calculated. In other words, when the photometric value correction process proceeds to step S305, the final photometric value can be determined without executing the photometric value calculation process. In this case, the processing load of the imaging device 100 can be reduced without performing unnecessary correction value calculation process.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these, and various modifications and variations are possible within the scope of the gist of the present invention. For example, in the above-described embodiment, an imaging device with an integrated optical lens was described, but a configuration that employs a lens-interchangeable imaging device in which so-called interchangeable lenses can be attached and detached may also be used.

In addition, in the above-described embodiment, the application of a correction value to a linear photometric value was mentioned, but the present invention is not limited to this, and a configuration in which a correction value is applied to a logarithmic photometric value may also be used. For example, a backlit scene was given as an example of a shooting scene in which correction to a linear photometric value is required, but an example of a shooting scene in which correction to a logarithmic photometric value is required corresponds to a case in which the main subject is highly luminous and the background is low luminance, such as the spotlight shooting described above.

When shooting with a spotlight, if the exposure is determined based on logarithmic photometry, the main subject illuminated by the spotlight may be overexposed and saturated due to the influence of low-brightness areas in the background.

Therefore, in a configuration in which exposure is determined based on a logarithmic photometric value, as described above, a configuration may be adopted in which the difference between the logarithmic photometric value and the linear photometric value is calculated, and the logarithmic photometric value is corrected according to the magnitude of the difference 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 from those in the first embodiment described above. In this case, the larger the difference value, the greater the first correction value becomes, and the greater the degree of correction becomes, so that the photometric value is corrected so that the exposure becomes brighter in dark shooting scenes.

The attenuation coefficient γ can be determined so that when the logarithmic photometric value is bright, the attenuation rate for the first correction value is high (the degree of correction is small). For example, the attenuation coefficient γ can 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.

In the above-described embodiment, linear and logarithmic photometric values are mentioned as the photometric values to be calculated, but the present invention can be applied to any embodiment in which separate photometric values are obtained based on two methods with different characteristics of the output relative to the input to the image sensor. For example, the present invention can be applied to any configuration in which photometric values are obtained with a different slope of the conversion characteristic relative to a linear conversion in which the input and output are one-to-one as the input/output characteristic. In this case, the directionality (underexposure side or overexposure side) of the correction value for the difference value (which can be an absolute value) changes depending on whether the conversion characteristic is steep or gradual for the photometric value obtained based on the conversion characteristic to be corrected.

In addition, in the above-described embodiment, a configuration in which the photometric value is calculated using the image sensor 116 has been described, but the present invention can also be applied to a case in which the photometric value is calculated using the image sensor 106. In other words, the present invention can also be applied to a configuration that has only an image sensor that acquires an image signal for recording.

In the above-described embodiment, a digital camera has been described as an example of an imaging device for implementing the present invention, but the present invention is not limited to this. For example, the present invention may be configured to employ imaging devices other than digital cameras, such as portable devices such as digital video cameras and smartphones, wearable devices, in-vehicle cameras, and security cameras.

1 Camera system 100 Imaging device 101 Overall control unit 106 Imaging element A
116 Image sensor B
200 Interchangeable Lenses

Claims (14)

An imaging means for imaging a subject and outputting the image;
a first photometry means for dividing an image obtained by the imaging means into a plurality of regions and obtaining photometric values of the plurality of regions by linear photometry;
a second photometry means for dividing an image obtained by the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions based on a photometry method having different slopes of a transformation characteristic with respect to a conversion characteristic of the logarithmic photometry or the linear photometry;
an evaluation value calculation means for calculating an evaluation value for determining exposure when capturing an image of a subject;
a correction value calculation means for calculating a correction value based on a difference value between a first photometric result obtained using the first photometric means and a second photometric result obtained using the second photometric means;
having
the second photometry means acquires a photometry value for the plurality of regions that is equal to or less than the photometry value acquired by the first photometry means when the luminance of the subject is the same;
The imaging apparatus according to claim 1, wherein the evaluation value calculation means calculates the evaluation value based on the first photometry result and the correction value. The correction value calculation means calculates a first correction value based on the difference value,
The imaging device according to claim 1 , characterized in that a calculation is performed so 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. The imaging device according to claim 2, characterized in that the correction value calculation means performs calculations so that the first correction value is larger when the difference value is larger than a second threshold value that is larger than the first threshold value than when the difference value is equal to or smaller than the second threshold value. The imaging device according to claim 3, characterized in that the correction value calculation means performs calculations so that the first correction value when the difference value is equal to or greater than the first threshold value and equal to or less than the second threshold value is a value between 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 larger than the second threshold value. 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;
5. The image pickup apparatus according to claim 2 , wherein the evaluation value calculation means calculates the evaluation value based on the first photometry result and the second correction value. The imaging device according to claim 5, wherein the first photometry result and the second photometry result are photometry values indicated by the brightness value of the subject, and the correction value calculation means calculates the second correction value by setting the attenuation coefficient closer to 0 as the first photometry result is a smaller photometry value and setting the attenuation coefficient closer to 1 as the first photometry result is a larger photometry value. The imaging device according to any one of claims 1 to 6, characterized in that the evaluation value calculation means calculates the evaluation value without using the correction value when a method is set in the imaging device in which the ranging area is selected by a manual operation by a user. The imaging device according to any one of claims 1 to 7, characterized in that the evaluation value calculation means calculates the evaluation value based on the first photometry result and the correction value when the area of the main subject occupying the entire screen is larger than a predetermined value. The imaging device according to any one of claims 1 to 8, characterized in that the evaluation value calculation means calculates the evaluation value without using the correction value when a face area is included in the screen. The imaging device according to any one of claims 1 to 9, characterized in that the logarithmic photometry has a conversion characteristic that logarithmically compresses the photometric values of the multiple regions. An imaging means for imaging a subject and outputting the image;
a first photometry means for dividing an image obtained by the imaging means into a plurality of regions and obtaining photometric values of the plurality of regions by linear photometry;
a second photometry means for dividing an image obtained by the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions based on a photometry method having different slopes of a transformation characteristic with respect to a conversion characteristic of the logarithmic photometry or the linear photometry;
an evaluation value calculation means for calculating an evaluation value for determining exposure when capturing an image of a subject;
a correction value calculation means for calculating a correction value based on a difference value between a first photometric result obtained using the first photometric means and a second photometric result obtained using the second photometric means;
having
the second photometry means acquires a photometry value for the plurality of regions that is equal to or less than the photometry value acquired by the first photometry means when the luminance of the subject is the same;
The imaging apparatus according to claim 1, wherein the evaluation value calculation means calculates the evaluation value based on the second photometry result and the correction value. A method for controlling an imaging device having an imaging means for imaging a subject and outputting an image, comprising the steps of:
a first photometry step of dividing an image obtained by the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions by linear photometry;
a second photometry step of dividing the image obtained by the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions based on a photometry method having different slopes of a transformation characteristic with respect to a conversion characteristic of the logarithmic photometry or the linear photometry;
an evaluation value calculation step of calculating an evaluation value for determining exposure when capturing an image of a subject;
a correction value calculation step of calculating a correction value based on a difference value between a first photometric result obtained in the first photometric step and a second photometric result obtained in the second photometric step;
having
In the second photometry step, when the luminance of the object is the same, a photometric value that is equal to or smaller than a photometric value obtained in the first photometry step is obtained for the plurality of regions;
a correction value calculating step of calculating the evaluation value based on the first photometry result and the correction value, A method for controlling an imaging device having an imaging means for imaging a subject and outputting an image, comprising the steps of:
a first photometry step of dividing an image obtained by the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions by linear photometry;
a second photometry step of dividing the image obtained by the imaging means into a plurality of regions and acquiring photometric values of the plurality of regions based on a photometry method having different slopes of a transformation characteristic with respect to a conversion characteristic of the logarithmic photometry or the linear photometry;
an evaluation value calculation step of calculating an evaluation value for determining exposure when capturing an image of a subject;
a correction value calculation step of calculating a correction value based on a difference value between a first photometric result obtained in the first photometric step and a second photometric result obtained in the second photometric step;
having
In the second photometry step, when the luminance of the object is the same, a photometric value that is equal to or smaller than a photometric value obtained in the first photometry step is obtained for the plurality of regions;
a correction value calculating step of calculating the evaluation value based on the second photometry result and the correction value, A computer-readable program for causing a computer to execute the imaging device control method according to claim 12 or 13.

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