Exposure amount determination device, exposure amount determination method, exposure amount determination program, and imaging device

Abstract

To absorb the relationship between an illuminance difference between an object to be photographed and a photographing device due to a change in the light source position by correcting an illuminance value according to the environment, and make it possible to obtain an image with appropriate brightness.SOLUTION: An exposure amount determination device according to the present invention that determines an exposure amount to be set in an imaging device includes an illuminance acquisition unit that acquires illuminance related to imaging by an imaging device, an illuminance correction unit that corrects an illuminance value from the illuminance acquisition unit according to the shooting environment, and an exposure amount derivation unit that derives an exposure amount to be set in the imaging device on the basis of the corrected illuminance value corrected by the illuminance correction unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exposure amount determination device, an exposure amount determination method, an exposure amount determination program, and an imaging device, and can be applied, for example, to an imaging device that photographs a subject (also called a "subject to be photographed") in an environment where the position of the light source changes. [Background technology]

[0002] For example, in order for an imaging device to acquire an image with appropriate brightness, the exposure is reduced when shooting in a bright environment and increased when shooting in a dark environment.

[0003] Patent Document 1 describes controlling exposure by linking the aperture, shutter speed, and amplifier gain according to the illuminance (brightness) of the shooting environment.

[0004] For example, the technology described in Patent Document 1 sets the maximum and minimum light intensity limits for auxiliary lighting in step S1. In step S2, if the current exposure value is dark, exposure control is performed in step S3 to brighten the subject's illumination by a correction amount obtained by multiplying the difference between the target exposure value and the current exposure value by the illumination light intensity control coefficient α. In step S4, if the required light intensity is less than the maximum light intensity, the required light intensity is used as the illumination light intensity after exposure control, and if an illumination light intensity exceeding the maximum light intensity is required, exposure correction is performed in step S5 to achieve the desired brightness. In step S2, the current exposure value is brighter than the target exposure value, and in step S6, if the required light intensity is greater than the minimum light intensity, the required light intensity is used as the illumination light intensity after exposure control in step S7, and if an illumination light intensity below the minimum light intensity is required, the auxiliary lighting is turned off in step S8. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-197499 [Overview of the project]

Problems to be Solved by the Invention

[0006] As described above, when taking an image, in order to obtain an image with appropriate brightness, it is necessary to change the exposure amount according to the brightness of the surface of the object to be photographed. Therefore, immediately before the target shooting, an image for exposure amount calculation is taken, and by calculating the brightness of the image, it is possible to obtain a more appropriate exposure amount.

[0007] However, the above-described conventional technology has a problem that the power consumption increases because it is necessary to execute shooting a plurality of times and also perform image analysis.

[0008] Also, it is possible to suppress power consumption by using an illuminance sensor or the like to acquire illuminance, deriving an exposure amount corresponding to the illuminance, and performing a single shooting. However, due to the positional relationship between the camera (imaging device), the illuminance sensor, the light source, and the subject, the brightness of the image may change significantly. That is, simply changing the exposure amount according to the output value of the illuminance sensor may not be able to obtain an image with appropriate brightness.

[0009] For example, FIG. 6(A) shows a case of shooting in front light, and FIG. 6(B) shows a case of shooting in back light.

[0010] The imaging device 1 has an illuminance sensor, and the illuminance sensor measures the illuminance value at the time of shooting. Also, as described above, generally, the image illuminance and the exposure amount at the time of shooting are in an inverse proportional relationship. When the illuminance value is high, the exposure amount is adjusted to be small, and conversely, when the illuminance value is low, the exposure amount is adjusted to be large so as to obtain an image with appropriate brightness.

[0011] As shown in Figure 6(A), when shooting in direct sunlight, the surface of the object being photographed is brighter than the lens surface of the imaging device. On the other hand, as shown in Figure 6(B), when shooting against the light, the surface of the object being photographed is darker than the lens surface of the imaging device. Therefore, even if you take a picture using the exposure amount obtained by directly using the illuminance value measured by the illuminance sensor, as in conventional methods, the resulting image will be dark.

[0012] Thus, a difference in illuminance occurs between the imaging device and the object being photographed. If the exposure amount is determined simply by inversely proportionality to the illuminance value and photography is performed, it may not be possible to obtain an image with appropriate brightness.

[0013] Therefore, in view of the above-mentioned problems, the present invention seeks an exposure amount determination device, exposure amount determination method, exposure amount determination program, and imaging device that can correct the illuminance value according to the environment, thereby absorbing the relationship between the illuminance difference between the object to be photographed and the imaging device due to changes in the position of the light source, and obtaining an image with appropriate brightness. [Means for solving the problem]

[0014] To solve these problems, the first invention provides an exposure amount determination device for determining the exposure amount to be set in an imaging device, wherein the imaging device This indicates the brightness of the light it captures. illuminance value An illuminance acquisition unit that acquires illuminance values ​​from the illuminance acquisition unit, They are distinguished by the magnitude of the illuminance value. Depending on the shooting environment Using the illuminance correction function The system is characterized by comprising an illuminance correction unit that corrects the illuminance, and an exposure amount derivation unit that derives the exposure amount to be set in the imaging device based on the corrected illuminance value corrected by the illuminance correction unit.

[0015] The second aspect of the present invention is an exposure amount determination method for determining the exposure amount to be set in an imaging device, wherein the illuminance acquisition unit is an imaging device This indicates the brightness of the light it captures. illuminance value The illuminance correction unit acquires the illuminance value from the illuminance acquisition unit, They are distinguished by the magnitude of the illuminance value. Depending on the shooting environment Using the illuminance correction function The system is characterized by correcting the exposure level and then having the exposure level derive unit derive the exposure level to be set on the imaging device based on the corrected illuminance value corrected by the illuminance correction unit.

[0016] The third aspect of the present invention is an exposure amount determination program for determining the exposure amount to be set in an imaging device, wherein a computer is used to determine the exposure amount to be set in the imaging device This indicates the brightness of the light it captures. illuminance value An illuminance acquisition unit that acquires illuminance values ​​from the illuminance acquisition unit, They are distinguished by the magnitude of the illuminance value. Depending on the shooting environment Using the illuminance correction function The system is characterized by having an illuminance correction unit that corrects the illuminance, and an exposure amount derivation unit that derives the exposure amount to be set in the imaging device based on the corrected illuminance value corrected by the illuminance correction unit.

[0017] The fourth aspect of the present invention is an imaging device for imaging an object to be photographed, characterized by comprising an exposure amount determination device of the first aspect of the present invention for determining the exposure amount related to imaging. [Effects of the Invention]

[0018] According to the present invention, by correcting the illuminance value according to the environment, the relationship between the illuminance difference between the object being photographed and the photographing device due to changes in the position of the light source can be absorbed, and an image with appropriate brightness can be obtained. [Brief explanation of the drawing]

[0019] [Figure 1] This is an internal configuration diagram showing the internal configuration of the imaging device according to the embodiment. [Figure 2] This is an overall configuration diagram showing the overall configuration of the image management system according to the embodiment. [Figure 3] This is a flowchart showing the overall operation of the imaging device according to the embodiment. [Figure 4] This is a flowchart showing the operation of the exposure amount determination process in the exposure amount determination device according to the embodiment. [Figure 5] This is an explanatory diagram illustrating an example of an illuminance correction function according to the embodiment. [Figure 6] This is an explanatory diagram illustrating that using the illuminance directly may not yield the appropriate exposure in the case of direct or backlighting. [Modes for carrying out the invention]

[0020] (A) Embodiment Hereinafter, embodiments of the exposure amount determination apparatus, exposure amount determination method, exposure amount determination program, and imaging apparatus according to the present invention will be described in detail with reference to the drawings.

[0021] (A-1) Configuration of the embodiment (A-1-1) An example of the overall structure Figure 2 is an overall configuration diagram showing the overall configuration of the image management system according to the embodiment. Note that the configuration of the image management system illustrated in Figure 2 is an example for explaining the embodiment and is not limited to what is shown in Figure 2.

[0022] The image management system 10 illustrated in Figure 2 has multiple imaging devices 1 (1-1 to 1-N; N is an integer) and a management server 2 connected via a network NT.

[0023] For example, in an environment with a light source 4 whose position changes over time, such as the sun (e.g., outdoors), each fixed imaging device 1 photographs the object to be photographed. In other words, each imaging device 1 photographs in an environment where the relative position between each fixed imaging device 1 and the light source 4 changes as the light source 4 moves.

[0024] The "object to be photographed" is assumed to be located in an open area, such as outdoors. The "light source 4" can be broadly applied, not limited to the sun, as long as its position changes over time. There may be one light source 4, or there may be multiple light sources, such as the sun and lighting devices. If there are multiple light sources 4, it is not necessary for the position of all of them to change; it is sufficient for the position of at least one of the multiple light sources 4 to change.

[0025] The imaging device 1 continuously or periodically photographs the object to be photographed. The shooting time (or shooting time) is not particularly limited, but in this embodiment, it is assumed that the imaging device 1 photographs the object to be photographed at multiple time points in time when the amount of light from the light source 4 hitting the imaging device 1 differs as the position of the light source 4 changes over time.

[0026] Furthermore, the imaging device 1 transmits information (e.g., packets) containing the captured images to the management server 2 via the network NT. Image transmission by the imaging device 1 involves sending information containing the images to the management server 2 each time the imaging device 1 captures an object. Alternatively, the imaging device 1 may be configured to transmit information containing multiple captured images to the management server 2 at a predetermined transmission time, such as once a day. In other words, the imaging device 1 may transmit images to the management server 2 each time an image is captured, or it may transmit images to the management server 2 in a batch process.

[0027] The management server 2 comprises a control unit 21, a storage unit 22, a communication unit 23, and a database unit 24. The management server 2 acquires information including images from each of the multiple imaging devices 1, and stores and manages the images for each imaging device 1 (or for each object being photographed).

[0028] The management server 2 sets various setting parameters related to the imaging of each imaging device 1, such as the imaging time (or time of imaging) and the transmission time for each imaging device 1. Regular It may also be configured to do so. For example, the management server 2 may send an illumination correction function corresponding to the environment in which the imaging device 1 is located to the corresponding imaging device 1 for it to set.

[0029] As described above, the image management system 10 is exemplified as being applicable to a monitoring system in which, for example, a target object located outdoors is photographed by each of several imaging devices 1, and each imaging device 1 transmits the captured images to a management server 2 for management.

[0030] However, the image management system 10 can be applied to various systems, not limited to the aforementioned monitoring system, as long as the imaging device 1 captures a subject in an environment that includes a light source 4 whose position changes over time. Furthermore, the image management system 10 can be used for a variety of services.

[0031] The example shown involves the imaging device 1 transmitting images to the management server 2 for storage, but the imaging device 1 may also store the captured images on a storage medium. In this case, the imaging device 1 does not need to be connected to the network NT. The imaging device 1 can be a wide variety of devices, such as general-purpose cameras, network cameras, surveillance cameras, or cameras built into smartphones, as long as it can capture images of the target object.

[0032] Management server 2 may be, for example, a cloud server, and each of the various functions of management server 2 may be distributed across different systems.

[0033] (A-1-2) Detailed description of the imaging device Figure 1 is an internal configuration diagram showing the internal configuration of an imaging device 1 according to an embodiment. In Figure 1, the imaging device 1 includes an exposure amount determination device 11, an imaging unit 12, an image signal processing unit 13, and an image output unit 14.

[0034] The imaging unit 12 can be an imaging device such as a camera, and includes an image sensor, lens, aperture, shutter, etc. The imaging unit 12 captures an image of the object to be photographed using the exposure amount value determined by the exposure amount determination device 11, and outputs the image data to the image signal processing unit 13. The aperture of the imaging unit 12 may be omitted.

[0035] The image signal processing unit 13 acquires the signal output from the image sensor of the imaging unit 12 and performs predetermined signal processing based on the signal from the image sensor. The image signal processing unit 13 converts the signal into data in a desired image data format and outputs it. The target image data format may be a commonly used method. Alternatively, the image signal processing unit 13 may output the signal from the imaging unit 12 directly to the image output unit 14 without performing any processing such as image data format conversion. In this case, the output data will be the raw data of the content of the signal output from the imaging unit 12.

[0036] The image output unit 14 outputs the image data output from the image signal processing unit 13 to the outside. For example, the image output unit 14 is a communication unit that forms and transmits packets containing image data in accordance with the communication protocol of Network NT.

[0037] Furthermore, when the imaging device 1 is used without being connected to the network NT, the image output unit 14 may output image data to a display device such as a liquid crystal screen. Alternatively, the image output unit 14 may output to a storage medium such as an SD card.

[0038] In Figure 1, the exposure amount determination device 11 includes an exposure amount determination method setting unit 111, an exposure amount determination unit 112, an illuminance acquisition unit 113, an illuminance correction function setting unit 114, and a corrected illuminance derivation unit 115.

[0039] The exposure amount determination device 11 can be implemented as a circuit device having a CPU, ROM, RAM, EEPROM, etc. The ROM stores an exposure amount determination program that can be read by the CPU. The exposure amount determination program causes the CPU (computer) to function as an exposure amount determination method setting unit 111, an exposure amount determination unit 112, an illuminance acquisition unit 113, an illuminance correction function setting unit 114, and a corrected illuminance derivation unit 115. The functions of the exposure amount determination device 11 are realized when the CPU executes the exposure amount determination program stored in the ROM.

[0040] Conventionally, the imaging unit analyzes the signals of each of the multiple images (image frames) it captures, performs signal processing, and determines the brightness of the image from the image luminance to derive the exposure value. However, this requires image signal processing, which results in a large processing load and high power consumption. It also takes a long time to process.

[0041] Furthermore, when the imaging device 1 captures an image, as described above, the image illuminance value and the exposure amount are inversely proportional. By utilizing this relationship and determining the exposure amount from the illuminance value measured by an illuminance sensor, the imaging device 1 can reduce power consumption and obtain an image with appropriate brightness. However, when the light source 4, such as the sun, moves, the relative position changes, causing the imaging device 1 to take pictures in front of or behind the light, which can significantly change the image brightness. In such cases, even by utilizing the inverse proportional relationship described above, it may not be possible to obtain an appropriate exposure amount from the illuminance value, and an image with appropriate brightness may not be obtained.

[0042] Therefore, the exposure amount determination device 11 in this embodiment converts the illuminance value acquired by the illuminance acquisition unit 113 using an illuminance correction function that converts the illuminance value according to the shooting environment, and derives an exposure amount value using the corrected illuminance value after conversion.

[0043] This allows the exposure amount to be determined from the illuminance value measured by the illuminance acquisition unit 113, such as an illuminance sensor, rather than through signal processing. This reduces the processing load and power consumption. Furthermore, it shortens the processing time.

[0044] Furthermore, by correcting the illuminance value using an illuminance correction function that corresponds to the shooting environment, it is possible to determine the appropriate exposure amount even in shooting environments where the position of light source 4 moves. As a result, an image with appropriate brightness can be obtained.

[0045] The exposure amount determination method setting unit 111 sets the exposure amount determination method to be adopted by the exposure amount determination unit 112. For example, multiple exposure amount determination methods are set in advance, such as the normal exposure amount determination method performed by the imaging unit 12 and the exposure amount determination method using a corrected value (corrected illuminance value) obtained by correcting the illuminance value measured by the illuminance acquisition unit 113 such as an illuminance sensor, and the exposure amount determination method setting unit 111 sets one of the multiple exposure amount determination methods to the exposure amount determination unit 112.

[0046] "The normal exposure determination method in the imaging unit 12" refers to the existing exposure determination method installed in the imaging unit 12. In other words, it is a method that does not perform illuminance value correction. Therefore, a detailed explanation is omitted here.

[0047] The "method for determining exposure amount using corrected illuminance values" is a method for deriving exposure amount using corrected illuminance values ​​corrected with an illuminance correction function, and will be explained in detail in the section on operation.

[0048] The exposure amount determination unit 112 determines the exposure amount value using the exposure amount determination method set by the exposure amount determination method setting unit 111, and sets the determined exposure amount value to the imaging unit 12. The operation mode in which the exposure amount is derived using the "normal exposure amount determination method" described above is called the "normal mode," and the operation mode in which the exposure amount is derived using the "exposure amount determination method using corrected illuminance value" is called the "corrected illuminance application mode."

[0049] The illuminance acquisition unit 113 acquires the illuminance value from the imaging device 1 and provides the acquired illuminance value to the corrected illuminance derivation unit 115. The illuminance acquisition unit 113 can use an illuminance sensor.

[0050] The illuminance sensor, which functions as the illuminance acquisition unit 113, measures the illuminance on the lens surface of the imaging unit 12. For example, the illuminance sensor measures the brightness of the light captured by the imaging unit 12, that is, the illuminance of the light that shines from the object being photographed toward the lens surface of the imaging unit 12.

[0051] The illuminance correction function setting unit 114 sets the illuminance correspondence relationship defined according to the shooting environment in the corrected illuminance derivation unit 115 in order to correct the illuminance.

[0052] Here, the illuminance correspondence is defined by determining multiple imaging environments (e.g., nighttime, daytime with front lighting, daytime with backlighting, etc.) according to the magnitude of the illuminance, and defining the illuminance conversion relationship for each shooting environment. In this embodiment, an illuminance correction function is given as an example of the illuminance correspondence, but it is not limited to this illuminance correction function.

[0053] The corrected illuminance derivation unit 115 uses an illuminance correction function, which is a set illuminance correspondence relationship, to correct the illuminance value from the illuminance acquisition unit 113 and derive a corrected illuminance value. The corrected illuminance derivation unit 115 provides the corrected illuminance value to the exposure amount determination unit 112.

[0054] (A-2) Operation of the embodiment Next, the operation of the imaging device 1 according to this embodiment will be described with reference to the drawings.

[0055] (A-2-1) Overall operation Figure 3 is a flowchart showing the overall operation of the imaging device 1 according to this embodiment.

[0056] In the imaging device 1, the exposure amount determination device 11 derives an exposure amount value to be applied to the imaging unit 12 (step S101), and provides that exposure amount value to the imaging unit 12. Details of this exposure amount derivation process will be described later.

[0057] The imaging unit 12 uses the exposure value from the exposure amount determination device 11 to photograph the object to be photographed and outputs the raw image data from the image sensor to the image signal processing unit 13 (step S102).

[0058] The image signal processing unit 13 converts the raw image data into output image data and provides it to the image output unit 14 (step S103).

[0059] Here, the raw image data is the raw data output by the image sensor, unlike commonly used file formats such as bitmap or JPEG. The output image data is image data in a format conforming to any image format. The image format of the output image data may be a commonly known image format. Note that step S103 may be omitted and the process may proceed to the next step. In this case, the image signal processing unit outputs the raw image data output from the imaging unit as output image data.

[0060] The image output unit 14 outputs the output image data from the image signal processing unit 13 to the outside (step S104).

[0061] (A-2-2) Exposure amount determination process Figure 4 is a flowchart showing the operation of the exposure amount determination process in the exposure amount determination device 11 according to the embodiment.

[0062] The exposure amount determination method setting unit 111 acquires the exposure amount determination method and provides the exposure amount determination method to the exposure amount determination unit 112 (step S201).

[0063] For example, the exposure amount determination method setting unit 111 can set either the normal exposure amount determination method in the imaging unit 12 or the exposure amount determination method using corrected illuminance values ​​to the exposure amount determination unit 112.

[0064] The exposure determination device 11 can employ various methods for switching the exposure determination method. For example, when using the imaging device 1 as an outdoor surveillance camera, an exposure determination method using corrected illumination values ​​can be set, while in other cases, the normal exposure determination method can be set. In this way, the exposure determination method can be switched according to the application of the imaging device 1 and the shooting environment, such as whether it is outdoors or indoors. Furthermore, the exposure determination method can be switched manually by the user or by control instructions from the management server 2.

[0065] The exposure amount determination unit 112 determines whether the exposure amount determination method set by the exposure amount determination method setting unit 111 is the corrected illumination application mode (or the normal mode) (step S202).

[0066] Then, if the exposure amount determination method is the normal exposure amount determination method, the exposure amount determination unit 112 determines that it is not the corrected illumination application mode (i.e., normal mode) (step S202 / No), and the exposure amount determination unit 112 determines the exposure amount using the imaging unit 12's normal exposure amount determination method (step S203). Then, in order to take a picture using the determined exposure amount, the exposure amount determination unit 112 outputs the determined exposure amount to the imaging unit 12 (step S208).

[0067] Furthermore, if the exposure amount determination method is an exposure amount determination method using a corrected illuminance value, the exposure amount determination unit 112 determines that it is in the corrected illuminance application mode (step S202 / Yes). At this time, for example, the exposure amount determination unit 112 requests the corrected illuminance derivation unit 115 to perform illuminance correction processing and proceeds to the process in step S204.

[0068] In the exposure amount determination device 11, the illuminance correction function setting unit 114 sets the illuminance correction function to be used for illuminance correction in the corrected illuminance derivation unit 115 (step S204).

[0069] For example, the illuminance correction function setting unit 114 has an illuminance correction function pre-set, and the illuminance correction function setting unit 114 sets this illuminance correction function to the corrected illuminance derivation unit 115. Also, since the characteristics of brightness (illuminance) illuminated by the light source 4 may differ depending on the change in the position of the light source 4, for example, an illuminance correction function may be pre-set for each season, month, etc., and the illuminance correction function setting unit 114 may select and set the illuminance correction function according to the current season, month, etc. to the corrected illuminance derivation unit 115. In other words, one or more illuminance correction functions may be set in the illuminance correction function setting unit 114, and the illuminance correction function setting unit 114 may select and set the illuminance correction function that is appropriate for the shooting situation and environment.

[0070] Next, the illuminance acquisition unit 113 measures and acquires the illuminance near the imaging device 1 that is illuminated by the light source 4 (step S205). The illuminance acquisition unit 113 provides the corrected illuminance value to the corrected illuminance derivation unit 115 in order to correct the measured illuminance value.

[0071] Then, the corrected illuminance derivation unit 115 uses the set corrected illuminance function to convert the illuminance value from the illuminance acquisition unit 113 to derive a corrected illuminance value (step S206), and the corrected illuminance derivation unit 115 provides the corrected illuminance value to the exposure amount determination unit 112.

[0072] The exposure amount determination unit 112 determines the exposure amount using the corrected illuminance value from the corrected illuminance derivation unit 115 (step S207). Then, in order to take a picture using the determined exposure amount, the exposure amount determination unit 112 outputs the determined exposure amount to the imaging unit 12 (step S208).

[0073] (A-2-3) Example of a corrected illuminance function Here, we will explain the corrected illuminance function with an example.

[0074] Figure 5 is an explanatory diagram illustrating an example of an illuminance correction function according to the embodiment. In Figure 5, the horizontal axis shows the measured illuminance [lx] measured by the illuminance acquisition unit 113, and the vertical axis shows the corrected illuminance [lx] after correction.

[0075] In the example in Figure 5, the illuminance correction function f n (x) shall be expressed by equations (1) to (4).

[0076] f n (x=a n ·x+b n (n=0,1,2)…(1) b0=c1(1-a0) (0 <x≦c1のとき、n=0)…(2) b1=c1(1-a1) (c1 <x≦c2のとき、n=1)…(3) b2=c1(1-a1)+c2(a1-a2)=b1+c2(a1-a2) (c2 <xのとき、n=2)…(4)

[0077] In equations (1) to (4), c m c0 is the brightness threshold (where m is an integer). The brightness threshold is the threshold used to determine the brightness of the shooting environment. Note that c0 indicates the minimum subject illumination required by the camera for shooting.

[0078] In this example, two threshold values c1 and c2 are set. For example, c1 is used to distinguish between an environment (extremely dark place) where the amount of light from the light source 4 is extremely small and dark, such as at night, and an environment where the amount of light is greater than that in the extremely dark place. Also for example, c2 is used to distinguish between environments with extremely high illuminance, such as daylight frontlight and daylight backlight.

[0079] In this example, by setting the light and dark threshold values, for example, when the measured illuminance is less than c1, it can be determined as "night", when the measured illuminance is greater than or equal to c1 and less than c2, it can be determined as "daylight frontlight", and when the measured illuminance is greater than or equal to c2, it can be determined as "daylight backlight", etc. Thus, not only can the brightness of the light source 4 be discriminated, but also the brightness that changes according to the positional relationship between the light source 4 and the illuminance sensor (illuminance acquisition unit 113) mounted on the imaging device 1 can be discriminated.

[0080] Also for example, by providing c1 and c2, three shooting environments such as "night", "daylight frontlight", and "daylight backlight" are distinguished, and in each of the shooting environments, the characteristics of the illuminance correction function for converting the measured illuminance value c t can be defined for each shooting environment. Examples are shown below.

[0081] For example, in equations (1) to (4), a0, a1, and a2 are illuminance coefficients and are parameters that determine the slope. In this example, the illuminance correction function f n (x) = x (that is, a n = 1) is set as the default.

[0082] When the measured illuminance value by the illuminance acquisition unit 113 is c1, when converting the measured illuminance value using the default illuminance correction function, the corrected illuminance value after conversion is set to be c1.

[0083] [When 0 < c t ≤ c1 (nighttime)] For example, when the measured illuminance value c t is within the range of 0 < c t ≤ c1, it is the case when the imaging device 1 takes a picture in an environment with low brightness illuminated by the light source 4, such as "night".

[0084] In this case, when it is desired to increase the image brightness and obtain a brighter image, the corrected illuminance derivation unit 115 selects the illuminance correction function a0>1, as exemplified in Figure 5.

[0085] Both the illuminance correction function a0>1 and the default illuminance correction function f0(x) (a0=1) pass through the point (c1,c1), but the slope of the illuminance correction function a0>1 is greater than the slope of the default illuminance correction function f0(x).

[0086] Therefore, the measured illuminance value c is obtained using an illuminance correction function where a0 > 1. t When converted, the corrected illuminance value after conversion is the measured illuminance value c t The value will be smaller than this. Also, since image illuminance and exposure amount are inversely proportional, the measured illuminance value c t The exposure value obtained using the corrected illumination value is greater than the exposure value obtained using the other method. Therefore, the imaging unit 12 can take a picture with a larger exposure value, and thus a brighter image can be obtained. The value of a0 can be determined appropriately as long as a0 > 1.

[0087] Conversely, the measured illuminance value c t 0 <c t When the value is within the range ≤ c1 and a darker image with lower brightness is desired, the corrected illuminance derivation unit 115 selects the illuminance correction function a0 < 1, as illustrated in Figure 5.

[0088] The illuminance correction function for a0<1 and the default illuminance correction function f0(x) both pass through the point (c1,c1), and the slope of the illuminance correction function for a0<1 is smaller than the slope of the default illuminance correction function f0(x).

[0089] Therefore, the measured illuminance value c is obtained using an illuminance correction function where a0 < 1. t When converted, the corrected illuminance value after conversion is the measured illuminance value c t The value will be greater than this. Therefore, the measured illuminance value c t The measured illuminance value c is greater than the exposure amount obtained using tUsing a larger corrected illuminance value results in a smaller exposure. Therefore, the imaging unit 12 can capture images with a smaller exposure value, thus obtaining images with lower brightness (darker images). Note that the value of a0 can be determined appropriately as long as a0 < 1, provided that a0 ≠ 0.

[0090] Regarding the method for determining whether to brighten or darken an image, various existing technologies can be applied, and one example will be described. For example, the image signal processing unit 13 can analyze the image brightness based on the image signal from the imaging unit 12 and determine whether to brighten or darken the image.

[0091] In other words, for example, the image signal processing unit 13 compares a threshold for determining the brightness (luminance) of an image with the luminance of the image captured by the imaging unit 12, and the image signal processing unit 13 determines the brightness of the image. Then, the corrected illuminance derivation unit 115 acquires the determination result of the image signal processing unit 13, and based on the determination result, a n Use the function >1, or a n The corrected illuminance derivation unit 115 may decide whether to use a function with a value of <1.

[0092] This method of determination can be similarly applied to other areas such as "daytime with direct sunlight" and "daytime backlighting."

[0093] [c1 <c t [If c² is ≤ c² (daytime direct sunlight)] For example, the measured illuminance value c t c1 <c t If it is within the range of ≤c2, it means that the imaging device 1 is taking a picture in a bright environment due to the light source 4, such as "daytime with direct sunlight".

[0094] In this case, when it is desired to increase the image brightness and obtain a brighter image, the corrected illuminance derivation unit 115 selects the illuminance correction function a1<1, as exemplified in Figure 5.

[0095] Both the illuminance correction function for a1<1 and the default illuminance correction function f1(x) pass through the point (c1,c1), but the slope of the illuminance correction function for a1<1 is smaller than the slope of the default illuminance correction function f1(x) (a1=1).

[0096] Therefore, the measured illuminance value c is obtained using an illuminance correction function where a1 < 1. t When converted, the corrected illuminance value after conversion is the measured illuminance value c t The value will be smaller than this. Therefore, the measured illuminance value c t The measured illuminance value c is higher than the exposure value obtained using t Using a smaller corrected illuminance value results in a larger exposure value. Therefore, the imaging unit 12 can capture images with a higher exposure, allowing for higher image brightness and a brighter image to be obtained.

[0097] Conversely, the measured illuminance value c t c1 <c t When the image brightness is within the range of ≤c2 and it is desired to reduce the image brightness and obtain a darker image, the corrected illuminance derivation unit 115 selects the illuminance correction function a1>1 as exemplified in Figure 5.

[0098] Both the illuminance correction function a1>1 and the default illuminance correction function f1(x) pass through the point (c1,c1), but the slope of the illuminance correction function a1>1 is greater than the slope of the default illuminance correction function f1(x).

[0099] Therefore, the measured illuminance value c is obtained using an illuminance correction function where a1 > 1. t When converted, the corrected illuminance value after conversion is the measured illuminance value c t The value will be greater than [value]. Therefore, the measured illuminance value c t The measured illuminance value c is higher than the exposure value obtained using t Using a larger corrected illuminance value results in a smaller exposure value. Therefore, the imaging unit 12 can capture images with a reduced exposure, allowing for a lower image brightness and the acquisition of a darker image. [c2 <c t (In the case of backlighting during the daytime) Measured illuminance value c t c2 <c t This occurs when the image sensor 1 is in a range where strong light from light source 4 illuminates the lens of the image sensor 1, such as in a "daytime backlit" environment, and the image sensor 1 is taking a picture. The illuminance correction function in this case is denoted as function f2(x).

[0100] "Daytime sunlight (c1 <c t The function f1(x) for "≦c2" and "daytime backlight (c2 <c t Since the function f2(x) in ) is intended to be continuous, when x=c2, both functions pass through the same point. That is, when x=c2, f1(c2)=f2(c2).

[0101] Also, in this example, "daytime direct sunlight (c1 <c t For the function f1(x) ≤ c², we prepared two types of functions: one for when a1 < 1 and one for when a1 > 1.

[0102] Therefore, "Daytime backlighting (c2 <c t )" is a function f1(x) related to the function f when a1 < 1 in "daytime direct sunlight". 21 (x) and the function f1(x) related to the function f1(x) when a1>1 in "before noon direct sunlight". 22 (x) is set.

[0103] function f 21 (x) is continuous with the function f1(x) when a1<1. For example, in the case of "daytime direct sunlight", after correcting the measured illuminance value using the function f1(x) when a1<1, the function f 21 You may also use (x).

[0104] function f 21 When using (x), if you want to increase the image brightness, the corrected illuminance derivation unit 115 selects a function where a2 < 1.

[0105] In this case, the slope of the function a² < 1 is the same as the function f a² = 1. 21The slope of (x) is made extremely small. This is to prevent the exposure from changing drastically when the image is backlit. In other words, the function f 21 Since the slope of the function a² < 1 in (x) is made extremely small, the corrected illuminance value will have an extremely small difference from the measured illuminance value, and the change in exposure will also be small.

[0106] Also, the function f 21 When using (x), if you want to lower the image brightness, the corrected illuminance derivation unit 115 selects a function a2>1. In this case, the slope of the function a2>1 is the same as the function f a2=1. 21 It is greater than the slope of (x). Therefore, the corrected illuminance value is the measured illuminance value c t This results in a larger value, allowing for a smaller exposure. In other words, by reducing the exposure, the difference in illuminance between the amount of light entering the imaging unit 12 from the light source 4 in backlit situations and the amount of light reflecting off the object and entering the imaging unit 12 can be absorbed, resulting in a more appropriate image.

[0107] On the other hand, function f 22 (x) is continuous with the function f1(x) when a1>1. For example, in the case of "daytime direct sunlight", after correcting the measured illuminance value using the function f1(x) when a1>1, the function f 22 You may also use (x).

[0108] function f 22 When using (x), if you want to increase the image brightness, the corrected illuminance derivation unit 115 selects a function where a2 < 1.

[0109] In this case, the slope of the function a² < 1 is the same as the function f a² = 1. 22 The slope of (x) is made smaller. Therefore, the corrected illuminance value will be smaller than the measured illuminance value, and the exposure will be increased.

[0110] Note that function f 22 The slope of the function (x) for a² < 1 is given by the function f 21 Similar to the function of (x) a² < 1, it may be made extremely small to minimize the change in exposure.

[0111] Also, the function f 22 When using (x), if you want to lower the image brightness, the corrected illuminance derivation unit 115 selects a function a2>1. In this case, the slope of the function a2>1 is the same as the function f a2=1. 22 It is greater than the slope of (x). Therefore, the corrected illuminance value is the measured illuminance value c t A larger value allows for a smaller exposure. In other words, in backlit situations, a smaller exposure can be achieved, resulting in a more suitable image.

[0112] [Variations of the illuminance correction function] The illumination correction function shown in Figure 5 is just one example and can be determined appropriately depending on the shooting environment.

[0113] The illuminance correction function illustrated in Figure 5 shows an example where two brightness thresholds (c1, c2) are set. However, the number of brightness thresholds can be one or three or more, and can be set appropriately according to changes in the positional relationship between the imaging device 1, the illuminance acquisition unit 113, and the light source 4. For example, the position of the sun as the light source 4 differs depending on whether it is in the Southern or Northern Hemisphere, the season, etc., and this also affects the measured illuminance value. Therefore, by setting an illuminance correction function according to the environment of the imaging device 1, the illuminance value can be corrected according to that environment.

[0114] The illuminance correction function exemplified in Figure 5 is expressed as a linear function (first-order function) in each region where the measured illuminance can take place, but it may also be a nonlinear function.

[0115] (A-3) Effects of the Embodiment As described above, according to this embodiment, it is not necessary to take multiple images and perform image analysis with a high processing load to determine the exposure amount, and the exposure amount can be determined based on the illuminance value measured by an illuminance acquisition unit such as an illuminance sensor, thus reducing power consumption.

[0116] Furthermore, according to this embodiment, by correcting the illuminance value according to the environment to obtain the exposure amount, the relationship between the illuminance difference between the object being photographed and the imaging device due to changes in the light source position can be absorbed, and an image with appropriate brightness can be obtained.

[0117] (B) Other embodiments Although various modifications have been mentioned in the embodiments described above, the present invention can also be applied to the following modified embodiments.

[0118] (B-1) In the embodiments described above, the imaging device 1 was explained on the premise that it is a component of the image management system 10, but the imaging device 1 may also be used as a standalone device independent of the system. In that case, this can be achieved by mounting a storage device for storing images on the imaging device 1. [Explanation of Symbols]

[0119] 10...Image management system, 1...Imaging device, 2...Management server, NT...Network, 4...Light source, 5...Subject, 11...Exposure amount determination device, 12...Imaging unit, 13...Image signal processing unit, 14...Image output unit, 21...Control unit, 22...Storage unit, 23...Communication unit, 24...Database unit, 111...Exposure amount determination method setting unit, 112...Exposure amount determination unit, 113...Illuminance acquisition unit, 114...Illuminance correction function setting unit, 115...Corrected illuminance derivation unit.

Claims

1. An exposure amount determination device that determines the exposure amount to be set in an imaging device, The imaging device includes an illuminance acquisition unit that acquires an illuminance value indicating the brightness of the light captured by the imaging device, An illuminance correction unit corrects the illuminance value from the illuminance acquisition unit using an illuminance correction function that corresponds to the shooting environment, which is distinguished by the magnitude of the illuminance value. An exposure amount derivation unit derives the exposure amount to be set in the imaging device based on the corrected illuminance value corrected by the illuminance correction unit. An exposure amount determination device characterized by comprising:

2. The exposure amount determination device according to claim 1, characterized in that the illuminance correction unit determines a plurality of shooting environments according to the magnitude of the illuminance, and converts the illuminance value to the corrected illuminance value using the illuminance correspondence relationship of each of the plurality of shooting environments.

3. The exposure amount determination device according to claim 2, characterized in that each of the plurality of shooting environments is an environment in which the illuminance changes due to the movement of the light source.

4. Each of the aforementioned multiple shooting environments is distinguished using one or more threshold values ​​for the illuminance value. The illuminance correction unit identifies the corresponding shooting environment by comparing the illuminance value from the illuminance acquisition unit with one or more thresholds, and corrects the illuminance value using the illuminance correspondence relationship of the identified shooting environment. The exposure amount determination apparatus according to feature 2.

5. The exposure amount determination device according to any one of claims 1 to 4, characterized in that the illuminance acquisition unit is an illuminance sensor, and the illuminance sensor acquires the illuminance of light in the direction from the object to be photographed to the imaging device.

6. An exposure amount determination method for determining the exposure amount to be set in an imaging device, The illuminance acquisition unit acquires an illuminance value indicating the brightness of the light captured by the imaging device. The illuminance correction unit corrects the illuminance value from the illuminance acquisition unit using an illuminance correction function that corresponds to the shooting environment, which is distinguished by the magnitude of the illuminance value. The exposure amount derivation unit derives the exposure amount to be set for the imaging device based on the corrected illuminance value corrected by the illuminance correction unit. A method for determining exposure amount, characterized by the features described above.

7. An exposure amount determination program for determining the exposure amount to be set for an imaging device, Computers, The imaging device includes an illuminance acquisition unit that acquires an illuminance value indicating the brightness of the light captured by the imaging device, An illuminance correction unit corrects the illuminance value from the illuminance acquisition unit using an illuminance correction function that corresponds to the shooting environment, which is distinguished by the magnitude of the illuminance value. An exposure amount derivation unit derives the exposure amount to be set in the imaging device based on the corrected illuminance value corrected by the illuminance correction unit. An exposure amount determination program characterized by functioning in this way.

8. In an imaging device that images an object to be photographed, An imaging apparatus characterized by comprising an exposure amount determination device according to claim 1, which determines the exposure amount for imaging.

Images