Luminance correction device, luminance correction method, and program

Abstract

A measured luminance acquisition unit (300) acquires a measured luminance, which is the luminance of a measurement surface (S) measured by using a luminance meter (2). A viewing angle acquisition unit (302) acquires a viewing angle (α) of the luminance meter (2). A measuring angle acquisition unit (304) acquires a measuring angle (θ), which is an angle formed by the normal (N) of the measurement surface (S) and the light reception axis (RA) of the luminance meter (2). A correction unit (308) corrects an error in the measured luminance with respect to an ideal luminance on the basis of the viewing angle (α) and the measuring angle (θ). The ideal luminance represents the luminance of the measurement surface (S) that is to be measured by using the luminance meter (2) when the measuring angle (θ) is set to 0° while the viewing angle (α) and a measuring distance (d), which is the distance between the luminance meter (2) and a measurement position (MP) on the measurement surface (S), are kept intact.

Description

Brightness correction device, brightness correction method, and program

[0001] The present disclosure relates to a brightness correction device, a brightness correction method, and a program.

[0002] 2. Description of the Related Art A luminance meter is known as an instrument for measuring the luminance of a measurement object such as a display or a lighting device.

[0003] When measuring the luminance of a surface to be measured from an oblique angle using a luminance meter, an accurate measurement value (hereinafter referred to as "measured luminance") may not be obtained.

[0004] When the surface to be measured satisfies Lambert's cosine law (i.e., when the surface to be measured is a Lambertian surface), the luminance of the surface measured by a luminance meter is considered to be constant regardless of the measurement angle between the normal to the surface and the emitted light. For example, the surfaces of displays and lighting devices can be considered to be Lambertian surfaces.

[0005] According to this law, when measuring luminance using a luminance meter, the surface being measured can be considered to be a Lambertian surface, and if the measurement distance, which is the distance between the luminance meter and the measurement position on the surface being measured, and the viewing angle are constant, the measured luminance obtained should be constant regardless of the measurement angle.

[0006] However, in reality, the surface to be measured can be considered a Lambertian surface, and even if the measurement distance and field of view are constant, the measured luminance obtained by a luminance meter may vary depending on the measurement angle. In other words, the above law that luminance is constant regardless of the measurement angle only holds true under the condition that the field of view is sufficiently small. However, luminance meters are equipped with optical systems, and due to their structure, they have a field of view that is not negligible. Therefore, the above law may not hold true when measuring luminance using a luminance meter.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a luminance correction device, a luminance correction method, and a program that can obtain accurate measured luminance even when using a luminance meter to measure the luminance of a surface to be measured from an oblique angle relative to the surface.

[0008] The luminance correction device of the present invention comprises a measured luminance acquisition means for acquiring a measured luminance, which is the luminance of a surface to be measured measured by a luminance meter; a field of view acquisition means for acquiring the field of view angle of the luminance meter; a measurement angle acquisition means for acquiring a measurement angle, which is the angle between a normal to the surface to be measured and the light-receiving axis of the luminance meter; and a correction means for correcting an error of the measured luminance with respect to an ideal luminance based on the field of view and the measurement angle, wherein the ideal luminance is the luminance of the surface to be measured that should be measured by the luminance meter when the measurement angle is set to 0 degrees and the field of view remains the same.

[0009] 5B is a diagram showing the configuration of a luminance measurement system including a luminance correction device according to an embodiment of the present invention. FIG. 5B is a diagram showing, in perspective, how the luminance of a surface to be measured is measured from the front of the surface when the viewing angle is sufficiently small. FIG. 5C is a diagram showing, in perspective, how the luminance of a surface to be measured is measured from an oblique angle when the viewing angle is sufficiently small. FIG. 5D is a diagram showing, in side view, how the luminance of a surface to be measured is measured from the front of the surface when the viewing angle is large. FIG. 5E is a diagram showing, in side view, how the luminance of a surface to be measured is measured from an oblique angle when the viewing angle is large. FIG. 5F is a diagram showing, in plan view, the measurement area of ​​FIG. 5B. FIG. 5G is a diagram showing the geometric relationship between the luminance meter and the surface to be measured in FIG. 5A. FIG. 5F is a flowchart showing the operation of a luminance correction device according to an embodiment of the present invention.

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] 1 is a diagram showing the configuration of a luminance measurement system 1 including a luminance correction device 3 according to an embodiment of the present invention. As shown in the figure, the luminance measurement system 1 includes a luminance meter 2 and a luminance correction device 3.

[0012] [Luminance Meter] The luminance meter 2 is a device for measuring the luminance of the measurement surface of an object to be measured. The object to be measured is, for example, a display or a light. The object to be measured is not limited to an object equipped with a light-emitting mechanism such as a display or a light, but may be an object without a light-emitting mechanism, such as the wall of a building. The luminance meter 2 is connected to the luminance correction device 3 described below, and outputs the measured luminance, which is the luminance of the measurement surface measured by the luminance meter 2, to the luminance correction device 3. The luminance meter 2 includes, for example, an optical system 20, a visibility correction filter 21, a photoelectric conversion unit 22, a finder 23, a control unit 24, a memory unit 25, an operation unit 26, and a display unit 27.

[0013] The optical system 20 is a mechanism for collecting light from the surface to be measured. Any configuration may be adopted for the optical system 20, and the optical system 20 may include, for example, one or more lenses, one or more apertures, and one or more mirrors. The optical system 20 includes a detection optical system for forming an image of the surface to be measured toward the photoelectric conversion unit 22, and a finder optical system for forming an image of the surface to be measured toward a finder 23 (described later). The optical system 20 determines the field of view of the luminance meter 2 (described later). Specifically, the field of view of the luminance meter 2 is determined by the focal length of the optical system 20, the size of the aperture, etc.

[0014] The visibility correction filter 21 converts the light collected by the optical system 20 into light having a wavelength distribution according to the visibility of humans.

[0015] The photoelectric conversion unit 22 converts the light that has passed through the visibility compensation filter 21 into an electrical signal. The photoelectric conversion unit 22 may be, for example, a photomultiplier tube (PMT), a silicon photodiode, or an avalanche photodiode.

[0016] The finder 23 is a sight window through which the user can visually view the image of the surface to be measured. The user can adjust the optical system 20 while looking through the finder 23 to focus on the surface to be measured.

[0017] The control unit 24 controls the optical system 20, the photoelectric conversion unit 22, etc., and converts the electrical signal output from the photoelectric conversion unit 22 into a digital value and transmits it to the brightness correction device 3. The control unit 24 may include, for example, an amplifier, an A / D converter, a microcomputer, etc.

[0018] The storage unit 25 is an information recording medium such as a read-only memory (ROM), a random access memory (RAM), or a hard disk, and is an information recording medium that stores programs executed by the control unit 24. The storage unit 25 may also function as a work memory for the control unit 24.

[0019] The operation unit 26 is a button, a touch panel, etc. that allows the user to perform various operations related to luminance measurement. The operation unit 26 outputs the content of the operation to the control unit 24 in response to the user's operation.

[0020] The display unit 27 is, for example, a liquid crystal display, an organic EL display, etc. The display unit 27 displays the measurement results and the like in accordance with instructions from the control unit 24.

[0021] The configuration of the luminance meter 2 is not limited to that described above. For example, the luminance meter 2 may further include various optical filters such as a neutral density filter. The luminance meter 2 may also include a spectroscope that separates the light from the surface to be measured into individual wavelength components. In other words, the luminance meter 2 may be a spectroradiometer.

[0022] [Luminance Correction Device] The luminance correction device 3 corrects the measured luminance, which is the luminance of the surface to be measured measured by the luminance meter 2. The luminance correction device 3 is realized by a commonly used computer. Specifically, the luminance correction device 3 includes a control unit 30, a memory unit 32, an input unit 34, and an output unit 36.

[0023] The control unit 30 is configured with a CPU (Central Processing Unit) and the like, and operates based on a program. For example, the control unit 30 operates as various functional units, such as a measured brightness acquisition unit 300, a viewing angle acquisition unit 302, a measured angle acquisition unit 304, a correction coefficient calculation unit 306, and a correction unit 308, which will be described later, depending on the program being executed.

[0024] The storage unit 32 is a ROM, RAM, hard disk, or the like, and stores various programs and data used by the control unit 30, and inputs and outputs this information to and from the control unit 30. The program that uses the brightness correction method according to this embodiment may be stored in a semiconductor memory or other computer-readable information storage medium, and is read from the medium by the computer that constitutes the brightness correction device 3.

[0025] The input unit 34 is a keyboard, a mouse, a touch panel, or the like, and is used by the user to operate the brightness correction device 3. The output unit 36 ​​is a display, a printer, or the like, and is used to show the processing results of the brightness correction device 3 to the user by displaying them on a screen, printing them, or the like.

[0026] [2. Theoretical Background] When a surface to be measured satisfies Lambert's cosine law, the luminance of the surface measured by a luminance meter is said to be constant regardless of the measurement angle between the normal to the surface and the emitted light (hereinafter, this law will be referred to as the "law of constant luminance"). Here, Lambert's cosine law states that the luminous intensity observed on the surface to be measured is directly proportional to the cosine of the measurement angle. A surface that satisfies Lambert's cosine law is called a Lambertian surface. For example, the surfaces of displays, lighting devices, etc. can be considered to be Lambertian surfaces.

[0027] According to the law of luminance constancy, when measuring luminance using a luminance meter, the surface being measured can be considered to be a Lambertian surface, and if the measurement distance, which is the distance between the luminance meter and the measurement position on the surface being measured, and the viewing angle are constant, the measured luminance obtained should be constant regardless of the measurement angle.

[0028] However, in reality, the surface to be measured can be considered a Lambertian surface, and even if the measurement distance and field of view are constant, the measured luminance obtained by a luminance meter may vary depending on the measurement angle. This is because the law of constant luminance only holds true when the field of view is sufficiently small. A luminance meter is equipped with an optical system, and due to its structure, has a field of view that is not negligible. Therefore, when measuring luminance using a luminance meter, the law of constant luminance may not hold true. Below, we will use Figures 2 to 5D to explain the cases when the law of constant luminance holds true when the field of view is sufficiently small, and the cases when the law of constant luminance does not hold true when the field of view is large.

[0029] (1) When the viewing angle is sufficiently small First, the case when the viewing angle is sufficiently small, i.e., when the law of luminance constancy holds, will be described with reference to Figures 2 and 3. In the following description, it is assumed that the luminance of the measurement surface S of the measurement object 4 is measured using the luminance meter 2 shown in Figure 1. It is also assumed that the measurement surface S can be considered to be a Lambertian surface.

[0030] (1-1) Measuring the Luminance of a Surface to be Measured from the Front of the Surface to be Measured FIG. 2 is a perspective view showing how the luminance of the surface to be measured S is measured from the front of the surface to be measured when the viewing angle is sufficiently small. Note that the luminance meter 2 is omitted from FIG. 2 . FIG. 2 shows how the luminance of the emitted light EL of the surface to be measured S, which is emitted from a measurement area MA in the direction normal to the surface to be measured S, is measured by the luminance meter 2. Note that for convenience of explanation, FIG. 2 shows only light emitted from the measurement position MP as the emitted light EL measured by the luminance meter 2, but in reality, all light emitted from the measurement area MA is measured as the emitted light EL by the luminance meter 2 (the same applies to FIGS. 3 to 5D ). Here, the measurement position MP is the intersection of the surface to be measured S and the light-receiving axis RA of the luminance meter 2.

[0031] The measurement area MA is the area of ​​the measurement surface S through which the measurement space MS passes. The measurement space MS is a space determined by the viewing angle of the luminance meter 2. In FIG. 2, the viewing angle is sufficiently small, so the measurement space MS has a cylindrical shape. Therefore, in FIG. 2, where the luminance meter 2 is directly facing the measurement surface S, the measurement area MA has a perfect circular shape.

[0032] Here, the luminous intensity of the outgoing light EL emitted from the measurement area MA in the direction normal to the measurement surface S is expressed as I ０ , the area of ​​the measurement area MA is A ０ Then, the measured luminance L measured by the luminance meter 2 is ０ is expressed by the following equation (1).

[0033]

[0034] When the focus of the optical system 20 of the luminance meter 2 is aligned (in focus) with the measurement position MP on the measurement surface S, the luminance meter 2 measures only the luminance of the outgoing light EL that is emitted from the measurement area MA of the measurement surface S. In Fig. 2, the optical system 20 of the luminance meter 2 is adjusted to be in focus at the measurement position MP on the measurement surface S (the same applies to Figs. 3 to 5D).

[0035] (1-2) When measuring the luminance of a surface to be measured from an oblique angle relative to the surface to be measured Figure 3 is a perspective view showing how the luminance of the surface to be measured S is measured from an oblique angle relative to the surface to be measured when the viewing angle is sufficiently small. Note that the luminance meter 2 is not shown in Figure 3. Figure 3 shows how the luminance of the surface to be measured S is measured by moving the luminance meter 2 relative to the normal line N of the surface to be measured S by an angle θ, while the measurement distance, which is the distance between the luminance meter 2 and the measurement position MP, and the viewing angle remain the same as in Figure 2. The angle θ is the measurement angle formed by the normal line N of the surface to be measured S and the light-receiving axis RA of the luminance meter 2.

[0036] Here, if the luminous intensity of the component of the emitted light EL emitted from the measurement area MA in the direction of angle θ with respect to the normal N of the measurement surface S is I, the measured luminance L measured by the luminance meter 2 is expressed by the following equation (2):

[0037]

[0038] The denominator of equation (2) (apparent area of ​​the measurement area MA) should be the product of the area A of the measurement area MA when the luminance meter 2 faces the measurement surface S from a direction shifted by an angle θ with respect to the normal N of the measurement surface S, and the cosine of the measurement angle θ. However, the area A of the measurement area MA when the luminance meter 2 and the measurement surface S are directly facing each other (see (1-1))０ This is because the luminance meter 2 is manufactured on the assumption that it will be used to measure luminance from the front of the surface to be measured.

[0039] Next, the luminous intensity I of the component of the outgoing light EL emitted from the measurement area MA in the direction of angle θ with respect to the normal N of the measurement surface S is calculated by the following equation (3). ⊥ is the luminous intensity of the component of the outgoing light EL emitted from the measurement area MA in the direction of the normal N of the measurement surface S.

[0040]

[0041] Luminous intensity I ⊥ is calculated by the following equation (4): ０ is the luminance of the emitted light EL emitted from the measurement area MA in the direction of the normal N of the measurement surface S when the luminance meter 2 and the measurement surface S are directly facing each other (see Figure 2), and A is the area of ​​the measurement area MA when the luminance meter 2 faces the measurement surface S from a direction shifted by an angle θ from the normal N of the measurement surface S.

[0042]

[0043] Here, the area A of the measurement area MA is calculated by the following formula (5): Since the measurement area MA is the area of ​​the measurement surface S through which the measurement space MS passes, in Fig. 3 where the luminance meter 2 faces the measurement surface S from a direction shifted by an angle θ with respect to the normal N of the measurement surface S, the measurement area MA has an elliptical shape.

[0044]

[0045] By substituting equations (4) and (5) into equation (3), the luminous intensity I is finally calculated as shown in the following equation (6): ０ It can be seen that it is equal to

[0046]

[0047] Then, by substituting equation (6) into equation (2), the following equation (7) is obtained.

[0048]

[0049] Finally, from equations (1) and (7), the following equation (8) is obtained.

[0050]

[0051] From the above, when the viewing angle is sufficiently small, the measured luminance does not change when measuring the luminance of the measurement surface S from a frontal perspective and when measuring the luminance of the measurement surface S from an oblique perspective. In other words, when the viewing angle is sufficiently small, the measurement surface S can be considered to be a Lambertian surface, and if the measurement distance and viewing angle are constant, the measured luminance remains constant regardless of the measurement angle θ.

[0052] (2) When the Viewing Angle is Large Next, the case when the viewing angle is large, that is, when the law of constant luminance does not hold, will be described with reference to FIGS. 4A to 5D.

[0053] (2-1) When measuring the luminance of a surface to be measured from the front of the surface to be measured Fig. 4A is a side view showing how the luminance of the surface to be measured S is measured from the front of the surface to be measured when the viewing angle is large. Fig. 4B is a perspective view showing how the luminance of the surface to be measured S is measured from the front of the surface to be measured when the viewing angle is large. Note that the luminance meter 2 is not shown in Fig. 4B.

[0054] 4A and 4B, because the viewing angle is large, the measurement space MS' is not cylindrical but conical, unlike the examples in Figures 2 and 3. The measurement area MA' is the area of ​​the measurement surface S through which the measurement space MS' passes, and therefore in Figures 4A and 4B, where the luminance meter 2 and the measurement surface S are directly opposed to each other, the measurement area MA' is a perfect circle.

[0055] Area A of measurement area MA' ０ The distance d′ can be calculated by the following equation (9): In the following equation (9), d is the measurement distance, and α is the viewing angle.

[0056]

[0057] Here, the luminous intensity of the outgoing light EL emitted from the measurement area MA' in the direction normal to the measurement surface S is I ０ ', the measured luminance L measured by the luminance meter 2０ ' is expressed by the following equation (10).

[0058]

[0059] (2-2) When measuring the luminance of the measurement surface from an oblique angle relative to the measurement surface Fig. 5A is a side view showing how the luminance of the measurement surface S is measured from an oblique angle relative to the measurement surface S when the viewing angle is large. Fig. 5B is a perspective view showing how the luminance of the measurement surface S is measured from an oblique angle relative to the measurement surface S when the viewing angle is large. Note that the luminance meter 2 is not shown in Fig. 5B.

[0060] 5A and 5B show how the luminance of the measurement surface S is measured by moving the luminance meter 2 relatively by an angle θ with respect to the normal N of the measurement surface S, while the measurement distance d, which is the distance between the luminance meter 2 and the measurement position MP, and the viewing angle α remain the same as in the cases of FIGS. 4A and 4B. The angle θ is the measurement angle formed by the normal N of the measurement surface S and the light-receiving axis RA of the luminance meter 2.

[0061] Here, if the luminous intensity of the component of the outgoing light EL emitted from the measurement area MA' in the direction of angle θ with respect to the normal line N of the measurement surface S is I', the measured luminance L' measured by the luminance meter 2 can be calculated by the following formula (11). The denominator of formula (11) (apparent area of ​​the measurement area MA') should be the product of the area A' of the measurement area MA' when the luminance meter 2 faces the measurement surface S from a direction shifted by angle θ with respect to the normal line N of the measurement surface S, and the cosine of the measurement angle θ. However, the area A' of the measurement area MA' when the luminance meter 2 and the measurement surface S are directly facing each other (see (2-1)) ０ The reason for this is as stated above.

[0062]

[0063] The luminous intensity I' is calculated by the following formula (12): ⊥ ' is the luminous intensity of the component of the outgoing light EL emitted from the measurement area MA in the direction of the normal N of the measurement surface S.

[0064]

[0065] Luminous intensity I ⊥is calculated by the following equation (13): ０ ' is the luminance intensity of the emitted light EL emitted from the measurement area MA' in the direction of the normal N of the surface S to be measured when the luminance meter 2 and the surface S to be measured are directly facing each other (see Figures 4A and 4B), and A' is the area of ​​the measurement area MA' when the luminance meter 2 faces the surface S to be measured from a direction shifted by an angle θ from the normal N of the surface S to be measured.

[0066]

[0067] Substituting equation (13) into equation (12) gives the following equation (14).

[0068]

[0069] The process of deriving the area A' of the measurement area MA' will be described below with further reference to Figures 5C and 5D. Figure 5C is a plan view of the measurement area MA' in Figure 5B. Figure 5D is a diagram showing the geometric relationship between the luminance meter 2 and the measurement surface S in Figure 5A. Note that the luminance meter 2 is not shown in Figure 5D.

[0070] As shown in Figure 5C, the measurement area MA' is the area of ​​the measurement surface S through which the measurement space MS passes, so in Figure 3, where the luminance meter 2 faces the measurement surface S obliquely, the measurement area MA' has an elliptical shape.

[0071] Here, if the major axis of the measurement area MA' is a and the minor axis is b, the area A' of the measurement area MA' can be calculated from the formula for the area of ​​an ellipse using the following equation (15).

[0072]

[0073] As shown in FIGS. 5C and 5D, when the major axis LA of the measurement area MA′ is divided into two at the measurement position MP, the portion LA closer to the luminance meter 2 is １ The length of l １ , the part LA far from the luminance meter 2 ２ The length of l ２ Let's say.

[0074] l １ and l ２Let us consider expressing the semimajor axis a and semiminor axis b of the measurement area MA′ using the following equation (16). First, the semimajor axis a can be expressed by the following equation (16).

[0075]

[0076] Next, the minor axis b is calculated using the equation of an ellipse. The intersection point between the perpendicular line PL of the major axis LA passing through the measurement position MP and the outside of the measurement area MA' is defined as X (see FIG. 5C). In a coordinate plane with the center C of the measurement area MA' as the origin, the major axis LA as the x-axis, and the minor axis SA as the y-axis, the coordinates of point X are expressed by the following equation (18).

[0077]

[0078] By substituting the coordinates of point X expressed by equation (17) into the equation of the ellipse, the following equation (18) is obtained.

[0079]

[0080] By substituting equation (16) into equation (18) and modifying it, the minor radius b expressed by the following equation (19) is obtained.

[0081]

[0082] Next, using the measurement distance d, the viewing angle α, and the measurement angle θ, １ and l ２ Here, let us consider the line LA １ and the outside of the measurement space MS′ １ The foot F of the perpendicular line dropped from the light receiving axis RA １ The distance between the measurement position MP and １ (See FIG. 5D). ２ and the outside of the measurement space MS′ ２ The foot F of the perpendicular line dropped from the light receiving axis RA ２ The distance between the measurement position MP and ２ In this case, l １ and l ２ are respectively expressed by the following equations (20) and (21).

[0083]

[0084]

[0085] Here, point P １ and point F １ Regarding the distance between the point P and the point P, the following equation (22) holds. ２ and point F ２ Regarding the distance between and , the following equation (23) holds.

[0086]

[0087]

[0088] From equations (22) and (23), d １ and d ２ can be expressed by the following equations (24) and (25), respectively.

[0089]

[0090]

[0091] By substituting the equations (24) and (25) into the equations (20) and (21), the following equations (26) and (27) are obtained.

[0092]

[0093]

[0094] By substituting equations (16), (19), (26), and (27) into equation (15) and rearranging it, the measured area A' expressed by the following equation (28) is obtained.

[0095]

[0096] By substituting equation (28) into equation (14), the luminous intensity I' expressed by the following equation (29) is obtained.

[0097]

[0098] Finally, by substituting equations (9) and (29) into equation (11), the following equation (30) is obtained from equation (10).

[0099]

[0100] From equation (30), when the viewing angle α is large, the measured luminance may change when measuring the luminance of the measurement surface S from a frontal perspective relative to the measurement surface S and when measuring the luminance of the measurement surface S from an oblique perspective relative to the measurement surface S. In other words, when the viewing angle α is large, the measurement surface S can be considered to be a Lambertian surface, and even if the measurement distance d and the viewing angle α are constant, the measured luminance may change depending on the measurement angle θ.

[0101] According to the brightness correction device 3 of this embodiment, the measured brightness L when measured from the front of the measurement surface S is ０ This allows correcting the error (see formula (30)) in the measured luminance L' when measured obliquely relative to the surface S to be measured, relative to the luminance L'. In other words, the luminance correction device 3 makes it possible to obtain an accurate measured luminance even when the luminance meter 2 is used to measure the luminance of the surface S to be measured obliquely relative to the surface S to be measured. The luminance correction device 3 will be described in detail below.

[0102] 3. Functions Realized by the Brightness Correction Device The brightness correction device 3 realizes a measured brightness acquisition unit 300, a viewing angle acquisition unit 302, a measurement angle acquisition unit 304, a correction coefficient calculation unit 306, and a correction unit 308. The measured brightness acquisition unit 300, the viewing angle acquisition unit 302, the measurement angle acquisition unit 304, the correction coefficient calculation unit 306, and the correction unit 308 are mainly realized by the control unit 30.

[0103] [Measured Brightness Acquisition Unit] The measured brightness acquisition unit 300 acquires the measured brightness, which is the brightness of the measurement target surface S measured by the brightness meter 2. The measured brightness acquisition unit 300 may acquire the measured brightness stored in the memory unit 25 of the brightness meter 2 and output from the brightness meter 2 to the brightness correction device 3, or may acquire the measured brightness manually input by the user via the input unit 34.

[0104] [Viewing Angle Acquisition Unit] The viewing angle acquisition unit 302 acquires the viewing angle α of the luminance meter 2 (see FIG. 5A etc.). The viewing angle acquisition unit 302 may acquire the viewing angle α stored in the storage unit 25 of the luminance meter 2 and output from the luminance meter 2 to the luminance correction device 3, or may acquire the viewing angle α manually input by the user via the input unit 34.

[0105] [Measurement Angle Acquisition Unit] The measurement angle acquisition unit 304 acquires the measurement angle θ, which is the angle between the normal N of the measurement target surface S and the light-receiving axis RA of the luminance meter 2 (see FIG. 5A , etc.). The measurement angle acquisition unit 304 may acquire the measurement angle θ stored in the memory unit 25 of the luminance meter 2 and output from the luminance meter 2 to the luminance correction device 3, or may acquire the measurement angle θ manually input by the user via the input unit 34.

[0106] [Correction Coefficient Calculation Unit] The correction coefficient calculation unit 306 calculates a correction coefficient K , which indicates the ratio between the ideal luminance and the measured luminance, based on the viewing angle α and the measurement angle θ. Ｃ The ideal luminance is the luminance of the measurement surface S that should be measured by the luminance meter 2 when the measurement angle θ is set to 0 degrees while the measurement distance d, which is the distance between the luminance meter 2 and the measurement position MP on the measurement surface S, and the viewing angle α remain the same (see FIGS. 4A and 4B). Specifically, the ideal luminance is expressed by equation (10).

[0107] Correction coefficient K Ｃ Specifically, the correction coefficient K is expressed by the following equation (31): Ｃ is the luminance L in equation (30). ０ ' is the reciprocal of the factor

[0108]

[0109] Correction coefficient K Ｃ can also be said to be the value obtained by multiplying the ratio of the measured area to the ideal measured area by the cosine of the measurement angle θ, or the value obtained by dividing the ratio of the measured area to the ideal measured area by the cosine of the measurement angle θ. The measured area is the area of ​​the measurement region MA' determined by the measurement distance d, the viewing angle α, and the measurement angle θ (see FIG. 5B), and is specifically expressed by equation (28). The ideal measured area is the area of ​​the measurement region when the measurement angle θ is set to 0 degrees while the measurement distance d and the viewing angle α remain the same (see FIG. 4B), and is specifically expressed by equation (9). In this embodiment, the correction coefficient K Ｃ is the ideal measurement area divided by the measured area, divided by the cosine of the measurement angle θ.

[0110] [Correction Unit] The correction unit 308 calculates a correction coefficient K Ｃ To be more specific, the correction unit 308 applies a correction coefficient KＣ By multiplying by , the error of the measured luminance relative to the ideal luminance is corrected.

[0111] 6 is a flowchart showing the operation of the brightness correction device 3 according to an embodiment of the present invention. The process shown in FIG. 6 is executed by the control unit 30 operating in accordance with a program stored in the storage unit 32.

[0112] Specifically, first, the control unit 30 acquires the measured luminance (S600). Next, the control unit 30 acquires the viewing angle α (S602) and the measurement angle θ (S604). The control unit 30 calculates the correction coefficient K based on the viewing angle α and the measurement angle θ. Ｃ (S606). Then, the control unit 30 calculates the correction coefficient K Ｃ to the measured luminance, thereby correcting the error of the measured luminance with respect to the ideal luminance (S608). Finally, the control unit 30 displays the correction result on the output unit 36 ​​(S610), and the process ends.

[0113] [5. Summary] According to the luminance correction device 3 of this embodiment described above, it is possible to correct the error of the measured luminance with respect to the ideal luminance, and therefore it is possible to obtain an accurate measured luminance even when the luminance of the measurement surface is measured obliquely using a luminance meter.

[0114] It should be noted that the present invention is not limited to the above-described embodiment. Furthermore, the specific character strings and numerical values ​​described above and the specific character strings and numerical values ​​in the drawings are merely examples, and the present invention is not limited to these character strings and numerical values.

[0115] For example, the correction coefficient K Ｃ may be the reciprocal of the value shown in equation (31). In this case, the correction unit 308 calculates the measured luminance by the correction coefficient K Ｃ Dividing by may correct for errors in the measured luminance relative to the ideal luminance.

Claims

1. A luminance correction device comprising: measurement luminance acquisition means for acquiring measurement luminance which is the luminance of a surface to be measured measured by a luminance meter; viewing angle acquisition means for acquiring the viewing angle of the luminance meter; measurement angle acquisition means for acquiring a measurement angle which is the angle formed by the normal line of the surface to be measured and the light receiving axis of the luminance meter; and correction means for correcting an error of the measurement luminance with respect to ideal luminance based on the viewing angle and the measurement angle, wherein the ideal luminance is the luminance of the surface to be measured to be measured by the luminance meter when the measurement angle is set to 0 degrees while the measurement distance which is the distance between the luminance meter and the measurement position on the surface to be measured and the viewing angle remain the same.

2. The luminance correction device according to claim 1, further comprising correction coefficient calculation means for calculating a correction coefficient indicating a ratio between the ideal luminance and the measurement luminance based on the viewing angle and the measurement angle, wherein the correction means corrects the error by applying the correction coefficient to the measurement luminance.

3. The correction coefficient is a value obtained by multiplying the ratio between the measurement area and the ideal measurement area by the cosine of the measurement angle or a value obtained by dividing the ratio between the measurement area and the ideal measurement area by the cosine of the measurement angle, wherein the measurement area is the area of a measurement region determined by the measurement distance, the viewing angle, and the measurement angle, and the ideal measurement area is the area of the measurement region when the measurement angle is set to 0 degrees while the measurement distance and the viewing angle remain the same. The luminance correction device according to claim 2.

4. The luminance correction device according to claim 3, wherein the measurement region is a region through which a conical measurement space determined by the viewing angle passes on the surface to be measured.

5. The luminance correction device according to claim 3 or 4, wherein the measurement region has an elliptical shape.

6. A luminance correction method comprising: a measurement luminance acquisition step of acquiring measurement luminance which is the luminance of a surface to be measured measured by a luminance meter; a viewing angle acquisition step of acquiring the viewing angle of the luminance meter; a measurement angle acquisition step of acquiring a measurement angle which is the angle formed by the normal line of the surface to be measured and the light receiving axis of the luminance meter; and a correction step of correcting an error of the measurement luminance with respect to ideal luminance based on the viewing angle and the measurement angle, wherein the ideal luminance is the luminance of the surface to be measured to be measured by the luminance meter when the measurement angle is set to 0 degrees while the measurement distance which is the distance between the luminance meter and the measurement position on the surface to be measured and the viewing angle remain the same.

7. A program for causing a computer to function as measurement luminance acquisition means for acquiring measurement luminance, which is the luminance of a surface to be measured measured by a luminance meter; field angle acquisition means for acquiring the field angle of the luminance meter; measurement angle acquisition means for acquiring a measurement angle, which is the angle formed by the normal line of the surface to be measured and the light receiving axis of the luminance meter; and correction means for correcting an error of the measurement luminance with respect to ideal luminance based on the field angle and the measurement angle, wherein the ideal luminance is the luminance of the surface to be measured to be measured by the luminance meter when the measurement distance, which is the distance between the luminance meter and the measurement position on the surface to be measured, and the field angle remain the same and the measurement angle is set to 0 degrees. Program.

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