WO2011142295A1 - Spectral reflectivity measuring device and spectral reflectivity measuring method - Google Patents

Abstract

Disclosed is a spectral reflectivity measuring device (1) provided with a reflection calibration plate (4), a plurality of optical filters (5) for transmitting light with different wavelengths therethrough, an image capturing unit (6), and a calculation processing unit (7). A plurality of images of an object to be measured (3) and the reflection calibration plate (4) are acquired while changing the optical filters (5). In the reflection calibration plate (4), a plurality of reflection calibration sections (4a) having different spectral reflectivities are formed, and the spectral reflectivities of the respective reflection calibration sections (4a) are known. In the calculation processing unit (7), the plurality of images of the object to be measured (3) and the reflection calibration plate (4), which are captured via the respective optical filters (5), are processed, and the spectral reflectivity of the object to be measured (3) is derived by a predetermined calculation.

Description

Spectral reflectance measuring apparatus and spectral reflectance measuring method

The present invention relates to a spectral reflectance measuring apparatus and a spectral reflectance measuring method capable of measuring a spectral reflectance of a measurement target.

Conventionally, in order to measure the spectral reflectance of an object to be measured, a spectral radiometer that can measure the intensity (energy) of incident light with respect to each wavelength has been used. Spectral reflectance is a characteristic related to how much light the wavelength of an object reflects, and in a general spectroradiometer, the spectral energy distribution of light reflected from the object to be measured is Measured. Since the spectral energy distribution is the product of the spectral energy distribution of the light source irradiating the object and the spectral reflectance, the spectral reflectance is obtained by dividing the measured value by the spectral energy distribution. Therefore, the spectral energy distribution of the light source needs to be known, but if this is unknown, a standard white plate that can reflect all wavelengths equally is placed in place of the object and the same measurement is performed. The spectral energy distribution of the light source.

The measurement using the above spectroradiometer measures a spectral reflectance at a certain point composed of a very small area to be measured. For this reason, for example, when measuring the spectral reflectance at each part of a measurement object having a two-dimensional spread, such as a picture, the measurement must be repeated one by one, and labor and time are required. There is a problem that it takes.

On the other hand, there is a multispectral camera as a device that can measure the spectral reflectance at each point of the measurement target having a two-dimensional spread (see Patent Document 1). A general multispectral camera is composed of a monochrome camera and a plurality of bandpass filters that transmit different wavelengths. In a multispectral camera, a bandpass filter is placed in front of a monochrome camera, and a measurement target is photographed through the bandpass filter. A plurality of images are acquired while sequentially replacing a plurality of bandpass filters that pass different wavelengths, and the incident energy of the wavelength region that passes through each bandpass filter can be calculated from the pixel values of each image. Yes. If this multispectral camera is used, the spectral energy distribution at each point to be measured can be measured by acquiring a plurality of images taken through different bandpass filters.

However, since this multispectral camera is a device that measures the energy distribution of incident light, when measuring the spectral reflectance of an object to be measured, the spectral energy distribution of the light source is similar to that of a spectroradiometer. Must be known.

In addition, the conventional spectroradiometer and multispectral camera described above are very expensive in equipment required for the apparatus. For example, in a spectroradiometer, a diffraction grating or a prism is used as a spectroscopic device, but these are generally expensive because they require precise processing. In addition, a bandpass filter used in a multispectral camera must be formed with a plurality of coating layers whose thicknesses are accurately controlled, which is expensive to manufacture and each piece is expensive.

The spectral characteristics of conventional spectroradiometers and multispectral cameras include the characteristics of light receiving elements such as diffraction gratings, bandpass filters, and CCDs used in cameras, and the amplification factor of the electronic circuit that processes the output of the light receiving elements. It depends on. Since these characteristics are easily affected by the usage environment such as the ambient temperature, it is necessary to take measures against the usage environment and aging may occur.To maintain accuracy, periodic calibration is required. is there.

JP 2002-185974 A

In view of the above-described points, an object of the present invention is to measure the spectral reflectance of a measurement object regardless of the spectral energy distribution of the light source and the characteristics of the imaging device, and to reduce the cost. To provide a reflectance measuring device and a spectral reflectance measuring method.

In order to solve the above problems and achieve the object of the present invention, a spectral reflectance measuring device of the present invention includes a reflection calibration plate, a plurality of optical filters, an imaging device, and an arithmetic processing device.
The reflection calibration plate has a plurality of reflection calibration sections having different spectral reflectances, and the spectral reflectance of each reflection calibration section is known. The plurality of optical filters are configured to have different spectral transmission characteristics. The imaging device captures a reflection calibration plate and a desired measurement object via each optical filter, generates a signal according to the amount of received light, and from the signal, the reflection calibration plate and An image of the measurement object is obtained. The arithmetic processing device processes a plurality of images of the measurement object and the reflection calibration plate photographed through each optical filter, and derives the spectral reflectance of the measurement object by a predetermined calculation.

In the spectral reflectance measuring apparatus of the present invention, a plurality of images of the reflection calibration plate and the measurement object are acquired through each of a plurality of optical filters having different spectral transmission characteristics. Then, the spectral reflectance of the measurement object is derived by processing these images with an arithmetic processing unit. In the spectral reflectance measuring apparatus of the present invention, the spectral reflectance of the measurement object can be obtained if only the spectral reflectance of the reflection calibration unit constituting the reflection calibration plate is known.

The spectral reflectance measurement method of the present invention has a plurality of reflection calibration units having different spectral reflectances, and captures a reflection calibration plate having a known spectral reflectance of each reflection calibration unit and a desired measurement object. And a step of preparing a plurality of optical filters each having different spectral transmission characteristics. And it has the process of image | photographing a measuring object and a reflection calibration plate through each optical filter with the imaging device through the same illumination conditions, and acquiring multiple images of a measuring object and a reflection calibration part. Furthermore, it has the process of deriving | assembling the spectral reflectance in a measuring object from the pixel value of the image of the measuring object acquired by the imaging device and the reflection calibration part with an arithmetic processing unit.

In the spectral reflectance measurement method of the present invention, since the spectral reflectance of the measurement object can be obtained from the pixel values of the image of the measurement object and the reflection calibration unit, only the spectral reflectance of the reflection calibration unit needs to be known. . For this reason, it is not necessary to know other optical filters, the sensitivity characteristics of the imaging device, and the like, and there is no need for calibration.

According to the present invention, the spectral reflectance of the measurement object can be measured regardless of the characteristics of the imaging device and the optical filter. Further, according to the spectral reflectance measuring apparatus of the present invention, the configuration is simple and an expensive member is not required, so that the cost can be reduced.

It is a schematic block diagram of the spectral reflectance measuring apparatus which concerns on one Embodiment of this invention. It is the figure which showed the measurement part 3a (illustrated by the spectral reflectance R ((lambda))) of the measuring object measured with the spectral reflectance measuring apparatus which concerns on one Embodiment of this invention. FIG. 5 is a diagram showing spectral reflectances (illustrated by r ₁ (λ) to r _m (λ)) of a reflection calibration unit formed on a reflection calibration plate of a spectral reflectance measurement apparatus according to an embodiment of the present invention. is there. A to D are measurement results of the spectral reflectances of the four types of measurement units 1 to 4 of the measurement object measured by the spectral reflectance measurement apparatus according to the embodiment of the present invention. It is a figure which shows the base (6 bases) which extends ideal measurement spectrum space.

Hereinafter, an example of a spectral reflectance measuring apparatus and a spectral reflectance measuring method according to an embodiment of the present invention will be described with reference to FIGS. In addition, this invention is not limited to the following examples.

[1. Spectral reflectance measuring device]
FIG. 1 shows a schematic configuration diagram of a spectral reflectance measuring apparatus according to an embodiment of the present invention. As shown in FIG. 1, the spectral reflectance measuring apparatus 1 according to the present embodiment includes a light source 2, a reflection calibration plate 4, an imaging device 6 that photographs a desired measurement object 3 and the reflection calibration plate 4, The optical filter 5 arrange | positioned at the light-incidence side of the imaging device 6 and the arithmetic processing apparatus 7 which performs a predetermined calculation are provided.

Light source 2 is for irradiating a desired and the measured object 3, light l ₁ in the reflective calibration plate 4. The light source 2 that can be used in the present embodiment is not particularly limited, and ambient light may be used. For this reason, the light source 2 may be a component of the spectral reflectance measuring apparatus 1 as in the present embodiment, but may not be. If the measurement object 3 and the reflection calibration plate 4 are kept bright enough to be photographed by the imaging device 6 at the time of measurement, the spectral reflectance measurement method of the present embodiment can be implemented. Further, the measurement object 3 and the reflection calibration plate 4 need to be arranged under the same illumination condition. That is, the measurement object 3 and the reflection calibration plate 4 are irradiated with the light ₁₁ having the same energy.

The reflection calibration plate 4 includes a plurality of reflection calibration units 4a having different spectral reflectances. The reflection calibration plate 4 that can be used in this embodiment is a spectral reflection unit of each reflection calibration unit 4a. Limited to those with known rates. Moreover, in the reflection calibration plate 4, the plurality of reflection calibration units 4a represent the spectral reflectance in each part of the measurement object 3 by linear combination of the spectral reflectances in each reflection calibration unit 4a for the arithmetic processing described later. Has been determined to be.

The imaging device 6 photographs the measurement object 3 and the reflection calibration plate 4 and is arranged so that the light l _r reflected from the measurement object 3 and the reflection calibration plate 4 is incident thereon. Although not shown, the imaging device 6 includes a CCD type or CMOS type image sensor, an optical lens that guides incident light to the image sensor, and a signal processing circuit that processes an output signal of the image sensor. In the imaging device 6, signal charges corresponding to the amount of light incident on the image sensor are generated. Then, the signal charge obtained by the photoelectric conversion is processed by the signal processing circuit, and an image is obtained.
In the present embodiment, a general CCD type digital single-lens reflex camera is used as the imaging device 6, and gamma correction is not performed in order to simplify the principle of a spectral reflectance measurement method described later. A black and white image shall be obtained.

The optical filter 5 is disposed on the light incident side of the imaging device 6, that is, on the front surface of an optical lens configured in a general imaging device. As a result, the light l _r reflected by the measurement object 3 and the reflection calibration plate 4 enters the imaging device 6 via the optical filter 5. In this embodiment, a plurality of optical filters 5 each having a different spectral transmission characteristic are prepared, and each optical filter 5 is replaced for each photographing.

The optical filter 5 used in the present embodiment does not need to be an expensive bandpass filter used in a conventional multispectral camera or the like, but uses an inexpensive color filter made of a film having a predetermined transmittance. be able to. That is, the plurality of optical filters 5 that can be used in the present embodiment only need to have different spectral transmission characteristics, and are excellent in monochromaticity designed to transmit only a specific wavelength range. It is not limited to. In addition, the optical filter 5 of the present embodiment may be a film that can transmit light within the wavelength range to be measured.
In this embodiment, a desired optical filter 5 was manufactured using a color filter manufactured by Edmund Optics. Further, the light transmission characteristics of each optical filter 5 do not need to be particularly known.

The arithmetic processing unit 7 is composed of, for example, a general computer, processes the images of the measurement object 3 and the reflection calibration plate 4 photographed by the imaging device 6, and performs spectral analysis at each part of the measurement object 3 by a predetermined calculation. The reflectance is derived. A method for deriving the spectral reflectance in the arithmetic processing unit 7 will be described later.

As described above, the spectral reflectance measuring apparatus 1 of the present embodiment has a simple configuration and does not require any particularly expensive equipment, and can be manufactured at low cost. For this reason, a significant cost reduction can be achieved as compared with conventional spectroradiometers and multispectral cameras.

[2. Spectral reflectance measurement method]
A spectral reflectance measuring method using the spectral reflectance measuring apparatus 1 of this embodiment will be described. The spectral reflectance measurement method of this embodiment, first, the measurement object 3 is irradiated with light l ₁ from the light source 2, installing the imaging device 6 so that it can photograph the measuring object 3 with the reflective calibration Version 4 .
Then, the measurement object 3 and the reflection calibration plate 4 are photographed through the optical filter 5 to obtain images of the measurement object 3 and the reflection calibration plate 4.

Here, the reflection calibration plate 4 and the measurement object 3 may be photographed simultaneously or separately. When the reflection calibration plate 4 and the measurement object 3 are photographed separately, the same light source 2 is used and photographing is performed with the same illuminance. That is, in this embodiment, if the reflection calibration plate 4 and the measurement object 3 can be photographed with the same brightness, the reflection calibration plate 4 and the measurement object 3 may be copied in one image. The reflection calibration plate 4 and the measurement object 3 may be copied on separate images.

This photographing is repeated while replacing the optical filter 5 to acquire the same number of images as the number of the optical filters 5. The obtained image may include an image taken without attaching the optical filter 5.
In this way, a plurality of images obtained while replacing the optical filter 5 are input to the arithmetic processing unit 7 and a calculation described later can be performed to obtain the spectral reflectance at each part of the measurement object 3.

[3. Spectral reflectance derivation method]
Hereinafter, calculation processing performed by the calculation processing device 7 will be described, and a method for deriving the spectral reflectance of the measurement object 3 will be described. FIG. 2 is a diagram showing a portion (hereinafter referred to as a measurement unit) 3a (illustrated by spectral reflectance R (λ)) to be measured of the measurement object 3 measured in the present embodiment. FIG. 3 is a diagram showing a reflection calibration section 4a (shown by spectral reflectances r ₁ (λ) to r _m (λ)) formed on the reflection calibration plate 4. In the present embodiment, the spectral reflectance R (λ) of the measuring unit 3a of the measuring object 3 is measured as a linear combination of the spectral reflectances r ₁ (λ) to r _m (λ) of each reflection calibrating unit 4a. The

First, the spectral reflectance in the measurement unit 3a of the measurement object 3 is R (λ), the spectral energy distribution of the light source 2 is I (λ), and the spectral sensitivity characteristic of the imaging device 6 including the optical filter 5 is f (λ). Then, the pixel value B of the pixel corresponding to the measurement unit 3a in the image obtained by photographing the measurement object 3 is expressed by the following [Equation 1]. Here, the “pixel value” is a value representing the brightness (light energy) of each pixel of the image obtained by the imaging device 6, and is a value proportional to the signal charge amount obtained by the image sensor of the imaging device 6. It is.

Where λ is the wavelength of light. In addition, the imaging device 6 used in this embodiment is set so that gamma in gamma correction is 1, that is, the pixel value is proportional to the intensity of light incident on the image sensor of the imaging device 6. Then, the product of I (λ) and f (λ) is replaced by the following [Equation 2].

Then, [Expression 1] becomes [Expression 3] below.

Taking an image by exchanging the plurality of optical filters 5 described in the above spectral reflectance measurement method generates pixel values B with different C (λ) in [Equation 3]. . A pixel value B generated with a different C (λ) is distinguished by using a subscript i, and C _i (λ) and B _i (i = 1, 2, 3,..., n). Here, n is the number of acquired images.
The purpose of this embodiment is to finally derive the spectral reflectance R (λ) in the measurement unit 3a of the measurement object 3 from the pixel value B _i acquired while replacing the optical filter 5.

As shown in FIG. 3, the reflection calibration plate 4 is a plate in which a plurality of reflection calibration units 4a having different spectral reflectances are partitioned and arranged, and the spectral reflectance of the reflection calibration unit 4a in the partition j is expressed as r. Let _j (λ) (j = 1, 2,..., m). Here, m is the number of reflection calibration units 4 a provided on the reflection calibration plate 4. Further, as described above, these spectral reflectances r _j (λ) are known. Further, the spectral reflectance R (λ) of the measurement unit 3a of the measurement object 3 to be obtained can be expressed by a linear combination of the spectral reflectances r _j (λ) of the reflection calibration unit, as shown in the following [Equation 4]. Assume that

Here, α _j is a linear combination coefficient. Assuming that it can be expressed by linear combination as in [Equation 4], the number of reflection calibration portions 4a formed on the reflection calibration plate 4 is increased, and the spectral reflectance r _j (λ) (j = 1, 2,...・ ・, M) It is fully satisfied by selecting the variation of m) appropriately. Calculating the B _i using Formula 3 and [Expression 4], [Equation 5] is obtained below.

However, b _ij is the following [ _Equation 6]. b _ij is a pixel value in the image i of the reflection calibration unit 4a in the section j of the reflection calibration plate 4 photographed simultaneously with the measurement object 3.

By calculating the coefficient α _j of [Equation 4] from the pixel value b _ij and the pixel value B _i of the measurement unit 3 a of the measurement object 3, the spectral reflectance R of the measurement unit 3 a of the measurement object 3 is finally obtained. (Λ) can be derived. Therefore, a method for obtaining α _j by [Equation 5] will be described.

First, the vectors x and y and the matrix M are defined as the following [Equation 7].

[Equation 5] can be expressed by the following [Equation 8] using [Equation 7].

The matrix M is generally not a square matrix and is not limited to full rank (rank (M) = min (m, n)). Therefore, as shown in the following [Equation 9], a solution of the coefficient x = (α ₁ α ₂ ... Α _m ) ^T (where T of the shoulder represents transposition) is obtained by a general inverse M ⁻ of M.

The calculation method of the general inverse M ⁻ of M is as shown in the following [Equation 10]. First, singular value decomposition of M is performed as follows.

Here, U is n × min (m, n), V is an orthogonal matrix of m × min (m, n), and Λ is a diagonal matrix of min (m, n) × min (m, n). is there. The general inverse M ⁻ is calculated by the following [Equation 11] using these matrices.

[Equation 11] lambda ^- is the diagonal matrix nonzero diagonal elements of lambda (specific values) and its inverse. However, in actual calculation, in consideration of the presence of an error, a value close to 0 is processed as 0.

Then, x = (α ₁ α ₂ ... Α _m ) ^T is calculated from [Equation 9] by the general inverse M ⁻ of M, and then α _j which is each element of x is _expressed by [Equation 4]. The target spectral reflectance R (λ) is derived by calculating as α _j .

That is, in the above-described calculation method, the pixel value B is obtained from the image of the measurement object 3, and the pixel value b is obtained from the image of each reflection calibration unit 4a of the reflection calibration plate 4. Then, a linear combination coefficient α is obtained from these pixel values B and b, and this is substituted into [Equation 4]. Thereby, the spectral reflectance R (λ) in the measurement unit 3a of the measurement object 3 is obtained. Therefore, in the present embodiment, the spectral energy distribution I (λ) of the light from the light source 2 and the spectral sensitivity characteristic f (λ) of the imaging device 6 including the optical filter 5 are measured by the measuring unit 3a of the measuring object 3. Does not contribute to the calculation of the spectral reflectance R (λ) at. For this reason, in this embodiment, it is not necessary to measure the energy distribution of the light emitted from the light source 2, and it is not necessary to calibrate the sensitivity characteristics of the optical filter 5 and the imaging device 6.

[Measurement result]
Next, a measurement result when a desired measurement object is actually measured by the spectral reflectance measurement apparatus 1 of the present embodiment will be shown. In this measurement, EOS Kiss digital X2 (trade name) manufactured by Canon Inc. was used as the imaging device 6 of the spectral reflectance measuring device 1, and was shot in a RAW image monochrome mode and stored in a 16-bit linear TIFF format. As the optical filter 5, # 10, # 16, # 19, # 23, # 41, # 55, # 57, # 64, filter color book NT39-417 (trade name) manufactured by Edmund Optics, Inc. Nineteen optical filters of # 66, # 73, # 86, # 88, # 92, # 93, # 96, # 313, # 346, # 386, and # 392 were used. In the measurement, a total of 20 images including 19 images captured using the optical filter 5 and one image captured without using the optical filter 5 were used. Further, as the reflection calibration section 4a of the reflection calibration plate 4, 19 sections of 2E to 2J, 3E to 3J, 4E to 4J, and 5E of the digital color checker SG (trade name) were used.

4A to 4D are measurement results of the spectral reflectance when measured using the spectral reflectance measuring apparatus 1 of the present embodiment and the spectral radiometer of the comparative example, and the horizontal axis indicates the wavelength (nm). The vertical axis represents the spectral reflectance. SR-3A (trade name) manufactured by Topcon Corporation was used as the spectroradiometer of the comparative example. In this measurement, the spectral reflectance is measured at four locations (measurement units 1 to 4) of the measurement target whose spectral reflectance is unknown by the spectral reflectance measuring apparatus 1 of the present embodiment and the spectral radiometer of the comparative example. Asked.

As can be seen from the measurement results of FIGS. 4A to 4D, the spectral reflectance measured by the spectral reflectance measuring apparatus 1 of the present embodiment shows almost the same value as the conventional spectral radiometer. That is, it was found that the spectral reflectance measurement apparatus 1 of the present embodiment can measure the spectral reflectance with almost the same accuracy as a conventional spectral radiometer with high measurement accuracy.

As described above, in the spectral reflectance measuring apparatus 1 according to the present embodiment, the spectral reflectances r _j (λ) (j = 1, 2,... Since m) is a measurement reference, it is not directly affected by the other optical filters 5 and the sensitivity of the imaging device 6 (sensitivity of the image sensor itself). For this reason, it is not necessary to calibrate the optical filter 5, the imaging device 6, and the like, and existing ones can be used as they are. Further, as described above, the light that irradiates the measurement object 3 and the reflection calibration plate 4 may be ambient light, and it is not necessary to prepare the light source 2 specially. When the light source 2 is used, a general halogen lamp or the like may be used, and the spectral energy distribution or the like need not be measured in advance. Thus, the spectral reflectance measuring apparatus 1 of the present embodiment can be formed with a simple configuration.

In the spectral reflectance measuring apparatus 1 of the present embodiment, even when measuring the spectral reflectance R (λ) in each part of the measurement object 3 having a two-dimensional spread, the entire image is acquired once. Then, the pixel value of each part of the measuring object 3 can be taken out in the image processing step. Therefore, the spectral reflectance R (λ) at each part can be obtained from the pixel value of each part of the measurement object 3 and the pixel value of the reflection calibration plate 4 in one measurement. For this reason, it is not necessary to measure point by point, and labor and time are not required.

By the way, in the present embodiment example, the procedure for measuring the spectral reflectance R (λ) of the measurement object 3 is as described above, but in designing the spectral reflectance measuring apparatus 1 of the present embodiment example, the reflection is performed. There is a degree of freedom in designing the spectral reflectance r _j (λ) of each reflection calibration unit 4 a of the calibration plate 4 and the spectral sensitivity characteristic f (λ) of the imaging device 6. In a typical situation, a set S _r of the spectral reflectance of the available reflective calibration unit 4a, from the set S _f sensitivity characteristic of the image pickup device 6 can be realized by the filter, so that choosing a set actually used . The preferred selection method will be described below.

First, here we evaluate the preference of measurement from two viewpoints. One viewpoint is how common the spectral reflectance space that can be expressed by the linear combination of r _j (λ) is. Another viewpoint is how much noise (error) is included in the measured result. For these two viewpoints, indices E _r and E _f representing how far away from the ideal are set, and r _j (λ) and the weighted sum E shown in the following equations are minimized. Select f (λ).

Here, c in [Equation 12] is a constant that balances the two criteria, and is set to an appropriate value according to the situation.
The index _Er regarding the space of the spectral reflectance that can be measured can be set as follows. As shown in FIG. 5, a preferable space for spectral reflectance that can be generally measured is considered to be a space stretched at the base having sensitivity at a certain interval with respect to the wavelength. Therefore, the distance from the preferable space that is actually stretched by r _j (λ) is defined as E _r . Specifically, it is calculated as follows. First, each function (ideal basis) shown in FIG. 5 is set to e _k (λ) (k = 1, 2,..., L), and r _j (λ) linearly expressing this optimally. _{Let the} coupling coefficient be γ _kj . This coefficient γ _kj can be solved by the following [ _Equation 13].

However, F _ji and G _kj are expressed by the following [ _Equation 14].

If E _rk is obtained by integrating the square of the difference between the actual basis e _k (λ) and the synthesized characteristic with the wavelength, E _rk is expressed by the following [ _Equation 15].

Since this E _rk is the reproducibility with respect to the base e _k (λ), it is calculated for each base. Therefore, in order to obtain an index within [Equation 12], it is preferable to take the sum of them or adopt the maximum value. Here, if the maximum value is taken, _{Er in} [Equation 12] is expressed by the following [Equation 16].

Here, as an example of an ideal spectral reflectance space, FIG. 5 shows an example of a base that divides the measurement range into six, but the space is not limited to six. Further, the space may not be based on the base so as to have sensitivity at regular intervals with respect to the wavelength.

Note that the amount of noise varies depending on the spectral distribution I (λ) of the light source and the spectral reflectance R (λ) of the measurement target. Therefore, these are represented by what seems to be average in the actual measurement situation. In addition, when it is difficult to assume that, it may be a constant value function (I (λ) = 1 and R (λ) = 1).

Once these functions are determined, the matrix M and the vector y of [Equation 7] can be calculated by [Equation 1] and [Equation 3], which are denoted as M ~ and y ~, respectively. From these, the spectral reflectance R (λ) calculated by [Equation 9] and [Equation 4] is R˜ (λ). Next, random numbers are added to each component of M ~ and y ~ assuming measurement noise. The random numbers to be added here are proper random numbers having an average of 0 and a fraction of 1. Similarly, after obtaining the spectral reflectance R (λ) according to [Equation 9] and [Equation 4] using the matrix M and the vector y added with random numbers, the difference from R˜ (λ) is squared to obtain the wavelength. The integrated D is obtained by the following [Equation 17].

Each time random numbers are added to the components of the matrix M ~ and the vector y ~, the average of [Equation 17] is calculated as shown in [Equation 18], and this is set as E _f of [Equation 12].

Here, although it is the number of D produced | generated in order to calculate an average, it is enough to produce | generate about 10,000 pieces, for example.
As described above, a set S _r of the available spectral reflectance and selecting candidates from the set S _f sensitivity characteristic of an imaging apparatus capable implemented by the available filters, for the candidate by [Equation 12] The evaluation value E can be calculated. In this way, the evaluation value E is calculated for various candidates, and the candidate with the smallest E is selected.

DESCRIPTION OF SYMBOLS 1 ... Spectral reflectance measuring device, 2 ... Light source, 3 ... Measurement object, 3a ... Measurement part, 4 ... Reflection calibration plate, 4a ... Reflection calibration part, ...・ Optical filter, 6... Imaging device, 7.

Claims (7)

A reflection calibration plate having a plurality of reflection calibration parts having different spectral reflectances, each spectral calibration part having a known spectral reflectance,
A plurality of optical filters each having different spectral transmission characteristics;
An imaging apparatus that photographs the reflection calibration plate and a desired measurement object through the optical filters, generates a signal corresponding to the amount of received light, and generates the reflection calibration plate from the signal. An imaging device for obtaining an image of the measurement object;
An arithmetic processing unit that processes a plurality of images of the measurement object and the reflection calibration plate photographed through each of the optical filters, and derives a spectral reflectance of the measurement object by a predetermined operation;
Spectral reflectance measuring device comprising: The spectral reflectance measurement apparatus according to claim 1, wherein the plurality of reflection calibration units are determined such that a spectral reflectance of the measurement object is represented by a linear combination of spectral reflectances in each reflection calibration unit. . In the arithmetic processing unit, when the spectral reflectance of the measurement object is represented by the linear combination of the spectral reflectances of the reflection calibration unit, a coefficient of linear combination is used as the pixel value of the measurement object and the plurality of reflection calibrations. Derived from the pixel value of the part,
The spectral reflectance measurement apparatus according to claim 2, wherein a spectral reflectance of the measurement object is derived from the derived linear combination coefficient. The spectral reflectance measuring device according to claim 3, further comprising a light source that irradiates the measurement object and the reflection calibration plate with light. A reflection calibration plate having a plurality of reflection calibration sections having different spectral reflectances, each of the reflection calibration sections having a known spectral reflectance, and an imaging device for photographing a desired measurement object, and different spectral transmission characteristics Preparing a plurality of optical filters having:
Using the imaging device, the measurement object and the reflection calibration plate are photographed through the respective optical filters under the same illumination condition, and a plurality of images of the measurement object and the reflection calibration unit are acquired. Process,
Deriving the spectral reflectance of the measurement object from the pixel value of the image of the measurement object acquired by the imaging device and the reflection calibration unit by an arithmetic processing device;
Spectral reflectance measurement method having In the step of deriving the spectral reflectance in the measurement object,
In the arithmetic processing unit, when the spectral reflectance of the measurement object is represented by the linear combination of the spectral reflectances of the reflection calibration unit, the linear combination coefficient is expressed as the pixel value of the measurement object and the plurality of reflection calibration units. And the pixel value of
The spectral reflectance measurement method according to claim 5, wherein a spectral reflectance of the measurement object is derived from the derived coefficient of the linear combination. The spectral reflectance measurement method according to claim 6, wherein the step of acquiring the image further includes a step of acquiring an image of the measurement object and the reflection calibration plate without using the optical filter.

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