JP2013052182A - Method for measuring cutaneous pigment concentration - Google Patents

Abstract

In measuring a pigment concentration from a skin image, the pigment concentration is accurately measured without being affected by a shadow formed in the image plane.
Based on a simulation model for calculating a spectral reflectance from a skin pigment concentration, an absorbance spectrum of a skin model containing each pigment such as melanin, oxidized hemoglobin, and reduced hemoglobin is expressed as each pigment concentration C _i (i = 1, 2, ..., N) are obtained for a plurality of different combinations, and the absorbance spectra of the obtained skin models are obtained as the extinction coefficient spectra ε _i (λ) (i = 1,2, ..., N) of each dye. Are used as explanatory variables to obtain regression parameters a _i (i = 1, 2,..., N). A relational expression between the regression parameter a _i (i = 1, 2,..., N) and the pigment concentration C _i (i = 1, 2,..., N) is obtained without using the regression parameter intercept a _0. , Using the relational expression, from the regression parameter a _i (i = 1, 2,..., N) of the absorbance spectrum of the subject's skin, each pigment concentration C _i (i = 1, 2,..., N) of the subject's skin. ) Is calculated.
[Selection] Figure 1

Description

  The present invention relates to a method for measuring skin pigment concentration and a method for forming a skin pigment image using this method.

  The apparent color of the skin depends on the type and concentration of pigments contained in the skin. Therefore, a method for measuring the concentrations of melanin, oxidized hemoglobin, and reduced hemoglobin contained in the skin based on observation of the color of the skin has been proposed.

  For example, from the Lambert-Beer law, the light absorption spectrum of the skin is modeled as a linear combination of the light absorption spectra of melanin, oxyhemoglobin, and reduced hemoglobin contained in the skin, and light is incident on an area of the skin. In addition, the so-called single-point measurement of the absorbance spectrum of the skin obtained as an average value by receiving the reflected light from the same region, by performing multiple regression analysis using the absorbance spectra of melanin, oxidized hemoglobin, and reduced hemoglobin, A method for determining the melanin concentration, oxidized hemoglobin concentration, or reduced hemoglobin concentration is known (Patent Document 1).

  However, this model is based on the premise that the absorbance spectrum is determined only by the absorption of the pigment in the skin, and the scattering at the epidermis or dermis constituting the skin and the scattering at each interface of the epidermis, dermis and subcutaneous fat are considered. The measurement accuracy of the dye concentration is low.

On the other hand, a multiple regression analysis method supplemented with a Monte Carlo simulation model considering scattering in the skin has been proposed (Non-Patent Document 1). In this assay, the absorbance spectrum by Monte Carlo simulation model and objective variable, melanin, oxyhemoglobin, and multiple regression analysis of the absorption coefficient spectra of reduced hemoglobin as explanatory variables, intercept a ₀ of the regression parameters, the regression parameters a _m melanin And a regression parameter a _th of total hemoglobin (where a _th = a _oh + a _dh , a _oh = regression parameter of the absorption coefficient spectrum of oxidized hemoglobin, a _dh = regression parameter of the reduced hemoglobin absorption spectrum), a ₀ , A _m and a _th , melanin concentration C _m and total hemoglobin concentration C _th , C _m = F _m (a ₀ , a _m , a _th ), C _th = F _th (a ₀ , a _m , a _th ) is obtained in advance.

On the other hand, the absorbance spectrum of any skin was _{subjected to} multiple regression analysis using the extinction coefficient spectra ε _m (λ), ε _oh (λ), and ε _dh (λ) of melanin, oxidized hemoglobin, and reduced hemoglobin as explanatory variables. An intercept a ₀ , a regression parameter a _m of the melanin extinction coefficient, and a regression parameter a _th of the total hemoglobin extinction coefficient are obtained, and this a ₀ , a _m , a _th and the above-mentioned relational expression C _m = F _m (a ₀ , a _m , a _th ) and C _th = F _th (a ₀ , a _m , a _th ), the melanin concentration C _m and the total hemoglobin concentration C _th are obtained.
In this method, the oxygen saturation C _StO2 = a _oh / (a _oh + a _dh ).

  The conventional pigment concentration measurement method using this Monte Carlo simulation model takes into consideration the influence of scattering on the absorbance spectrum of the skin, so that the measurement accuracy of the pigment concentration is high. However, in order to investigate the pigment concentration in the skin area with a certain extent, applying the conventional pigment concentration measurement method using the Monte Carlo simulation model to the pigment concentration measurement method using the skin image, When there is a shadow in the image plane due to illumination unevenness or the like, the measurement accuracy of the dye density is lowered due to the influence of the shadow.

JP-A-11-299743

Journal of Biomedical Optics 9 (4): 700-710 (2004)

  The present invention is intended to solve the above-described conventional problems, and in measuring the pigment concentration from a skin image, a method capable of accurately measuring a pigment density without being affected by the presence of a shadow in the image plane. It is also an object of the present invention to provide a skin pigment image that accurately represents the pigment concentration distribution of the skin.

When the skin image is not shaded, the inventor obtained the absorbance spectrum obtained by imaging the skin, the absorption coefficient spectrum ε _m (λ) of melanin, the absorption coefficient spectrum ε _oh (λ) of oxidized hemoglobin, and the absorption spectrum of reduced hemoglobin. Since the regression parameter intercept a ₀ obtained by multiple regression analysis with the coefficient spectrum ε _dh (λ) reflects the concentration information and skin scattering information of each pigment, the regression parameter intercept a ₀ is used. When the relational expression between the regression parameter and the pigment concentration is obtained, the pigment concentration can be obtained accurately. On the other hand, when there is a shadow in the skin image, the regression parameter is not used without using the regression parameter intercept a _0. The relationship between the regression parameter and the pigment concentration was found to eliminate the influence of the shadow information, and the absorbance spectrum of any skin was determined. By determining the skin pigment concentration from the regression parameters obtained by multiple regression analysis of the Torr with the absorption coefficient spectrum of the pigment and the above-mentioned relational expression, the pigment concentration is not affected by the shadow formed on the skin image. Has been found to be required accurately.

That is, according to the present invention, based on a simulation model for calculating the spectral reflectance from the skin pigment concentration, the absorbance spectrum of a skin model including a plurality of pigments is represented by the absorption coefficient spectrum ε _i (λ) (the pigment type of each pigment). N = i = 1, 2,..., N (the same applies hereinafter), and a plurality of cases where the combinations of the dye concentrations C _i (i = 1, 2,. Absorption spectra of the skin model are obtained by the following multiple regression equation (1) by performing multiple regression analysis using the extinction coefficient spectra ε _i (λ) (i = 1, 2, ..., N) of each dye as explanatory variables. Multiple sets of regression parameters a _i (i = 1, 2,..., N)

From the plurality of regression parameters a _i (i = 1, 2,..., N) and the plurality of dye concentrations C _i (i = 1, 2,..., N), the relational expression F in the following equation (2) _i (i = 1,2, ..., N)

On the other hand, the absorbance spectrum of the subject's skin is obtained, and the absorbance spectrum is subjected to multiple regression analysis using the extinction coefficient spectrum ε _i (λ) (i = 1, 2,..., N) of each dye as an explanatory variable. A regression parameter a _i (i = 1, 2,..., N) of the absorbance spectrum of the skin of the subject is obtained, and this regression parameter a _i (i = 1, 2,..., N) and the above-described relation F _i (i = 1, 2,..., N), a skin pigment concentration measurement method for obtaining at least one of a plurality of pigment concentrations C _i (i = 1, 2,..., N) of the skin of a subject is provided.

Further, the present invention obtains at least one pigment concentration of each pigment concentration C _i (i = 1, 2,..., N) for each pixel of the internally reflected light image of the subject's skin by the above-described method, A method of forming a skin pigment image that forms a distribution image of the pigment concentration is provided.
Furthermore, the present invention provides a skin pigment image thus formed.

  According to the present invention, based on a skin image, the concentration distribution of each pigment such as melanin, oxidized hemoglobin, and reduced hemoglobin in the skin can be accurately determined without being affected by the shadow formed on the image. Therefore, the relationship between the appearance when the skin is observed and the pigment concentration in the skin can be understood. Further, it is possible to easily analyze the oxygen saturation of hemoglobin, and it is possible to estimate the oxygen consumption state, blood circulation state, and the like in the skin. Furthermore, the skin pigment image of the present invention is taken over time for the skin to which the cosmetic is applied, and the effectiveness of the cosmetic is evaluated, for example, by examining changes in the concentrations of melanin, oxidized hemoglobin, and reduced hemoglobin. Is possible. The present invention is also useful for skin diagnosis for beauty at a store.

FIG. 1 is an example of an imaging system for obtaining a spectral reflection spectrum from an internally reflected light image of a subject. FIG. 2 is an explanatory diagram of a flow for _obtaining relational expressions F _m , F _oh and F _dh between the dye concentrations C _m , C _oh and C _dh and the regression parameters a _m , a _oh and a _dh . FIG. 3 is an image of regression parameters a _m , a _oh, a _dh and a ₀ obtained by the methods of the examples and comparative examples. FIG. 4 is an explanatory diagram of a method for forming a shadow on an image. FIG. 5 is a melanin image and a total hemoglobin image of Examples and Comparative Examples.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol represents the same or equivalent component.

In the method for measuring skin pigment concentration according to the present invention, in order to determine the pigment concentration in the subject's skin from the absorbance spectrum A (λ) of the subject's skin, first, based on a simulation model of the skin, various pigments are variously added to the skin. Absorbance spectrum A (λ) in the case where it is contained at a concentration C _i (i = 1, 2,..., N), and this absorbance spectrum A (λ) is determined as the extinction coefficient spectrum ε _i (λ) of each dye. Multiple regression analysis is performed using (i = 1, 2,..., N) as explanatory variables. For example, when melanin, oxygenated hemoglobin, and reduced hemoglobin are considered as pigments in the skin, the absorbance spectrum A (λ) based on the skin simulation model, the absorption coefficient spectrum ε _m (λ) of melanin, and the absorption coefficient of oxygenated hemoglobin Multiple regression analysis is performed using the spectrum ε _oh (λ) and the extinction coefficient spectrum ε _dh (λ) of reduced hemoglobin as explanatory variables to obtain the following multiple regression equation (1) _a .

Then, the regression parameters a _m obtained by the equation (1) _a, of a _oh, a _dh and its intercept a _o, without the use of sections a _o, the regression parameters a _m, a _oh, melanin from a _dh The relational expressions F _m , F _oh and F _dh of the following equation (2) _a for _{obtaining the} concentration C _m , the oxygenated hemoglobin concentration C _oh and the reduced hemoglobin concentration C _dh are obtained.

The sections a _o of multiple regression equation (1) _a, melanin, oxyhemoglobin, believed to contain density information of each dye of reduced hemoglobin, further, since there is no wavelength dependence, Ya light scattering in the dermis It is believed that information on skin scattering at the interface between the dermis and subcutaneous tissue is included. Therefore, an absorbance spectrum is obtained for combinations of various concentrations c _i (i = 1, 2,..., N) of pigments such as melanin and hemoglobin, and the regression parameters a _i (i (i)) of the pigment concentration and multiple regression equation (1) are obtained. = 1, 2,..., N) or a relational expression F thereof with an intercept a _o, and on the other hand, a regression parameter a _i or its intercept a _o is obtained by multiple regression analysis of an arbitrary absorbance spectrum. When obtaining the pigment concentration c _i from the obtained regression parameter a _i or intercept a _o and the above-mentioned relational expression F, a Monte Carlo simulation model is used, and the regression parameter of the extinction coefficient spectrum ε _m (λ) of melanin is used as the regression parameter. in a _m and conventional dye concentration measuring method using the regression parameters a _th of extinction coefficient spectrum epsilon _th of total hemoglobin (lambda) (non-Patent Document 1), a relational expression F, intercept a _o of the regression parameters including It was rare. In contrast, the present invention is that this relationship, the above equation that contains no sections a _o of the regression parameters (2), more specifically above when considering as a dye, melanin, hemoglobin oxidation, and reduced hemoglobin the following equation (2) _a relation F _m, F _oh, using the F _dh.

As a result, when the absorbance spectrum is obtained from the captured image, even if the image is shaded, the darkness of the image is not accurately measured as the effect of absorption / scattering inside the skin, and the dye concentration is accurately measured. Can be measured. This intercept a _o of the regression parameter, since there is no wavelength dependence, if that could shade the image, presumably because shading information is summarized in this section a _o.

Furthermore, the dye concentration in the conventional dye concentration measuring method using a Monte Carlo simulation model (Non-Patent Document 1) C _m, in the case of obtaining the C _oh and C _dh, is simply excluding sections a _0, a dye concentration C _m , C _oh whereas a three and C _dh, since the multiple regression parameters only two a _m and a _th, although accuracy for the three-to-two correspondence decreases, a _th If a _oh and a _dh are used instead of, three kinds of multiple regression parameters can be made to correspond to each other, so that a decrease in accuracy can be avoided.

  In the present invention, as described above, the relational expression (2)

First, based on the simulation model for calculating the spectral reflectance from the skin pigment concentration, the absorbance spectrum of the skin model containing a plurality of pigments is converted to the extinction coefficient spectrum ε _i (λ) (i = 1 , 2, ..., N).

As this simulation model, for example, Monte Carlo simulation (L.-H. Wang, SL Jacques, and L.-Q. Zheng, Computer Methods and Programs in Biomedicine 47, 131-146 (1995).) Can be used. . The Monte Carlo simulation is a model in which light incident on the skin is scattered, absorbed, and diffusely reflected with a probability according to the effective scattering coefficient and the absorption coefficient. For example, as shown in FIG. 2, when considering melanin, oxyhemoglobin, and reduced hemoglobin as this dye, the effective scattering coefficient spectrum (μs ′ (λ)) and the absorption coefficient spectrum of each melanin, oxyhemoglobin, and deoxyhemoglobin dye. The spectral reflectance R (λ) can be obtained from ε _m (λ), ε _oh (λ), ε _dh (λ), and the concentrations C _m , C _oh , and C _{dh of} the respective dyes.

More specifically, in this skin model,
The attenuation coefficient of the skin is expressed as C _m × ε _m (λ),
The attenuation coefficient of the dermis is expressed as C _oh × ε _oh (λ) + C _dh × ε _dh (λ).

Literature values can be used for the effective scattering coefficient spectrum (μs ′ (λ)) and extinction coefficient spectra ε _m (λ), ε _oh (λ), and ε _dh (λ) of each dye. By setting the densities C _m , C _oh , and C _dh , the spectral reflectance R (λ) at the set dye density can be obtained.

In the present invention, the simulation model for calculating the spectral reflectance from the skin pigment concentration is not limited to the Monte Carlo simulation. For example, the Kubelka-Munk formula, the Adding-Doubling method (Adding-Doubling method) method), diffusion theory, and models based on actual measurements using simulated skin.
A model based on Monte Carlo simulation is preferable because of the accuracy of the phenomenon description and the high consistency between the obtained spectra.

The spectral reflectance R (λ) thus obtained is converted into an absorbance spectrum by the absorbance spectrum A = log (1 / R), and further the extinction coefficient spectrum ε _m (λ of each pigment of melanin, oxidized hemoglobin, and reduced hemoglobin. ), Ε _oh (λ), ε _dh (λ) are used as explanatory variables, and multiple regression analysis is performed as in equation (1) _a to obtain regression parameters a _m , a _oh and a _dh and an intercept a ₀ .

The concentration C _m of the dye, C _oh and C _dh and the regression parameters a _m, a a _oh and a _dh, obtained for various combinations of dye concentration C _m, C _oh and C _dh, dye concentration C _m, C _oh , C _dh and regression parameters a _m , a _oh, and a _dh , F _m , F _oh , and F _dh are obtained.

  As a specific acquisition method of the relational expression, for example, polynomial approximation can be performed as in the following expression.

As a method for _obtaining the relational expressions F _m , F _oh , and F _dh of the dye concentrations C _m , C _oh, and C _dh and the regression parameters a _m , a _oh, and a _dh, it is possible to use a lookup table instead of polynomial approximation. Appendices, linear approximation, exponential function approximation, logarithmic function approximation, etc. may be used.

In the present invention, the relational expressions F _m , F _oh , and F _dh shown in FIG. 2 described above are obtained when there are other pigments in the skin, for example, when carotene, bilirubin, AGEs, etc. are present. (2) can also be obtained.

On the other hand, in the method of the present invention, an absorbance spectrum of the subject's skin is obtained separately from the above-described relational expression F _i (a ₁ , a ₂ ,..., A _N ). The method for obtaining the absorbance spectrum may use a so-called single-point spectral reflectance measurement device that makes light of a predetermined wavelength incident on a narrow region of the skin and uses an average value of reflected light received from the region, From the viewpoint of easy observation of the metabolism and blood circulation state of the skin, it is preferable to obtain by imaging the internal reflection light of the skin.

  For example, as in the imaging system shown in FIG. 1, light is incident on the subject 1 from the light source 3 through the first polarizing filter 2a, and the digital camera 5 passes through the wavelength variable filter 4 including the second polarizing filter 2b. Take an image. In this case, by making the polarization directions of the first polarizing filter 2a and the second polarizing filter 2b orthogonal, the second polarizing filter 2a shields the surface reflected light from the skin of the subject 1, and the skin color information is obtained. Only the internally reflected light to be carried is received by the digital camera 5.

  As the light source 3, a halogen lamp that emits white light, a metal halogen lamp, or the like is used. The light source 3 may emit parallel light or diffuse light. According to the method of the present invention, the pigment concentration in the skin can be accurately measured regardless of the shadow in the acquired image. Therefore, even a light source that forms a shadow on the subject can be used. Preferably, the one that emits light to the skin of the subject 1 within an incident angle range of 0 to 45 ° is used.

  The wavelength tunable filter 4 changes the transmission wavelength under the control of the controller 6. Thereby, for example, the internally reflected light image is repeatedly taken while shifting the imaging wavelength from the wavelength of 500 nm to 20 nm. In this case, it is preferable to align the sensitivity for each wavelength region based on the brightness of the white plate.

  As the digital camera 5, a monochrome camera is sufficient as long as the camera has sensitivity over the entire measurement wavelength region, but a color camera may be used.

  The image thus captured by the digital camera 5 is stored in the arithmetic device 7 such as a personal computer. The arithmetic unit 7 calculates the reflectance for each pixel from the pixel value of each pixel. When a color camera is used for photographing, a weighted average of RGB pixel values may be used as the pixel value, and only specific pixels having sensitivity to the measurement wavelength may be used. In the arithmetic unit 7, in order to calculate the spectral reflectance from the pixel value, using a programming environment capable of image processing, a coefficient for converting the pixel value of the white plate into the reflectance for each wavelength is obtained. A coefficient may be applied to the entire wavelength image. As such a programming environment, MATLAB (manufactured by Mathworks) or the like can be used.

The arithmetic unit 7 converts the spectral reflectance into an absorbance spectrum, and further performs multiple regression analysis using the absorption coefficient spectrum ε _i (λ) (i = 1, 2,..., N) of each dye as an explanatory variable. Regression parameters a _i (i = 1, 2,..., N) are calculated.

In addition, the arithmetic unit 7 includes a relationship between the above-described dye concentration C _i = F _i (a ₁ , a ₂ ,... A _N ) and the regression parameter a _i (i = 1, 2,..., N). formula

Are stored, and each dye concentration C _{i is} calculated from this relational expression (2) and the regression parameters a _i (i = 1, 2,..., N) calculated from the spectral reflectance obtained from the internally reflected light image of the subject. It is preferable to be able to calculate (i = 1, 2,..., N). More specifically, when considering melanin, oxygenated hemoglobin, and reduced hemoglobin as pigments, the above formula (2) _a

From the regression parameters a _m , a _oh and a _{dh of the} pigments of melanin, oxygenated hemoglobin and reduced hemoglobin, the pigment concentrations C _m , C _oh and C _dh of melanin, oxygenated hemoglobin and reduced hemoglobin are calculated.

Furthermore, one or any combination of each pigment concentration C _i (i = 1, 2,..., N) calculated for each pixel of the subject's skin image may be displayed in all pixels to form a skin pigment image. preferable. The skin pigment image thus obtained is not affected by the shadow and shows an accurate concentration distribution of the pigment.

  Hereinafter, the present invention will be specifically described based on examples.

Example 1 and Comparative Example 1
With the imaging system shown in FIG. 1, the internal reflection light image of the skin on the inner side of the forearm of the subject was photographed at intervals of 20 nm between wavelengths of 500 nm to 600 nm to obtain the spectral reflectance. In this case, the light sources placed on the left and right sides of the camera were installed so as to illuminate the measurement site as evenly as possible so that the image was not shaded. In addition, VariSpec (manufactured by CRi) was used as the wavelength tunable filter.

The obtained spectral reflectance is _{subjected to} multiple regression analysis using the extinction coefficient spectrum ε _m (λ) of melanin, the extinction coefficient spectrum ε _oh (λ) of oxidized hemoglobin, and the extinction coefficient spectrum ε _dh (λ) of reduced hemoglobin as explanatory variables. Thus, the regression parameters a _m , a _oh , a _dh and the intercept a _m0 were calculated. In this case, the values described in the following documents are used for the extinction coefficient spectrum ε _m (λ) of melanin, the extinction coefficient spectrum ε _oh (λ) of oxyhemoglobin, and the extinction coefficient spectrum ε _dh (λ) of reduced hemoglobin. It was. The regression parameters thus obtained are shown in FIG.

IEEE Trans. Biomed. Eng. 36 (1989) 1146-1154
http://omlc.ogi.edu/news/jan98/skinoptics.html
http://omlc.ogi.edu/spectra/
SPIE Proc. 3252 (1998) 70-82
J. et al. Invest Dermatol 77, 1 (1981) 13-19

  On the other hand, using the calculation software “MCML” (Computer Methods and Programs in Biomedicine 47: 131-146 (1995)), the spectral reflectance spectrum of a skin model containing melanin, oxidized hemoglobin and reduced hemoglobin is converted to a Monte Carlo simulation model (Journal of Biomedical). Optics 9 (4): 700-710 (2004)) and further converted to an absorbance spectrum.

In this case, the skin model has an epidermis thickness of 0.006 cm and a dermis thickness of 0.494 cm. The epidermis contains melanin and the dermis contains hemoglobin.
The refractive index of the epidermis and dermis was constant at 1.4.
The spectral wavelength was set to 6 conditions of 500, 520, 540, 560, 580, and 600 nm.
The melanin concentration is 10 conditions every 1% between 1-10%, the hemoglobin concentration is 5 conditions every 0.2% between 0.2-1.0%, and the oxygen saturation is between 0-100%. Six conditions were set every 20%. Here, the melanin concentration is a ratio when the concentration is 100% when the absorbance is equal to the absorbance of melanosomes given in Journal of Photochemistry and Photobiology Vol.53 No.6 769-775. Oxidized and reduced hemoglobin concentrations are ratios when the blood oxygen saturation of hematocrit 45% is 100% and the concentration when 0% is 100%.

Therefore, the reflectance of 6 × 10 × 5 × 6 = 1800 conditions is calculated, the spectral reflectance of 10 × 5 × 6 = 300 conditions is obtained, and the dye concentration and regression parameters of 10 × 5 × 6 = 300 conditions are obtained. By obtaining a pair and performing quadratic polynomial approximation, the relationship between the regression parameters a _m , a _oh and a _dh and the dye concentrations C _m , C _oh and C _dh C _m = F ¹ _m (a _m , a _{oh, a dh), C oh} = F 1 oh (a m, a oh, a dh), C oh = F 1 oh (a m, a oh, were obtained a _dh) (example 1).

Similarly, using the regression parameters, a _m , a _th (a _th = a _oh + a _dh ), a ₀ , the relational expression C _m = F ² _m (a _m , a _th , a ₀ ), C _th = F ² _th (a _m , a _th , a ₀ ) was obtained (Comparative Example 1).

FIG. 3 (upper) shows the intercept a ₀ and regression parameters a _m , a _oh and a _dh obtained from the skin image of the subject (common to Example 1 and Comparative Example 1). From the Monte Carlo simulation, it is expected that the intercept a ₀ takes a value of approximately 0.13 to 0.43. On the other hand, in the vicinity of the center of the image in Example 1 or Comparative Example 1, the intercept a ₀ was about 2.3. The value of this a _0, since deviates larger than the value of the intercept a ₀ by Monte Carlo simulations, supra, the value of the intercept a ₀ reflects the unintended shading due to the influence of skin irregularities and lighting It is thought that there is.

From the relational expressions F ¹ _m , F ¹ _oh , F ¹ _dh , F ² _m , F ² _{th for obtaining} the dye concentrations in Example 1 and Comparative Example 1, respectively, and the regression parameters shown in FIG. For each of Example 1 and Comparative Example 1, the melanin concentration and the total hemoglobin concentration were determined. This melanin concentration and total hemoglobin concentration were determined and displayed in all pixels of the image. This is shown in FIG. From FIG. 5, the melanin concentration and the total hemoglobin concentration are measured by any of the methods of Example 1 and Comparative Example 1, but the image of Comparative Example 1 is out of focus. This is because the measurement site of Example 1 and Comparative Example 1 did not intentionally form a shadow, but because of the fine shadow caused by the skin condition, imaging conditions, etc., the melanin concentration in the method of Comparative Example 1 Or because the total hemoglobin concentration is not accurately measured.

Example 2 and Comparative Example 2
When taking an image in the first embodiment, as shown in FIG. 4, a crescent-shaped shield 8 is placed between the subject 1 and one of the two light sources arranged on the left and right of the camera. A clear shadow (a crescent moon-shaped shadow) was intentionally added to the image photographed in Step 5, and Example 1 and Comparative Example 1 were repeated using this shaded image. Note that the measurement site of the subject is the same as in Example 1.

FIG. 3 (lower row) shows regression parameters (common to Example 2 and Comparative Example 2) obtained from the skin image of the subject with shading. From the figure, it can be seen that in the shaded image, the influence of the given shadow appears in the regression parameter intercept a ₀ , which indicates that the intercept a ₀ does not correctly reflect the pigment concentration.

Example 2 and Comparative Example from the regression parameters in FIG. 3 (lower) and the respective relational expressions F ¹ _m , F ¹ _oh , F ¹ _dh , F ² _m , and F ² _th obtained in Example 1 and Comparative Example 1 A melanin concentration of 2 and total hemoglobin concentration were determined for all pixels of the image and are shown in FIG. From FIG. 5, according to Comparative Example 2, the shadow of the shielding object 8 is reflected in both the melanin image and the total hemoglobin image, and the pigment concentration is not correctly measured. It can be seen that it has been completely removed.

DESCRIPTION OF SYMBOLS 1 Test subject 2a 1st polarizing filter 2b 2nd polarizing filter 3 Light source 4 Wavelength variable filter 5 Digital camera 6 Controller 7 Computing device 8 Shielding object

Claims (7)

Based on the simulation model for calculating the spectral reflectance from the skin pigment concentration, the absorbance spectrum of the skin model including a plurality of pigments is expressed as the extinction coefficient spectrum ε _i (λ) of each pigment (i = 1, 2, ..., N, the same shall apply hereinafter), and the absorbance spectra of the obtained skin models are obtained for a plurality of cases where each combination of pigment concentrations C _i (i = 1, 2, ..., N) is different. By performing multiple regression analysis using the extinction coefficient spectrum ε _i (λ) (i = 1, 2,..., N) of each dye as an explanatory variable, a regression parameter a _i ( i = 1,2, ..., N)
From the plurality of regression parameters a _i (i = 1, 2,..., N) and the plurality of dye concentrations C _i (i = 1, 2,..., N), the relational expression F in the following equation (2) _i (i = 1,2, ..., N)
On the other hand, the absorbance spectrum of the subject's skin is obtained, and the absorbance spectrum is subjected to multiple regression analysis using the extinction coefficient spectrum ε _i (λ) (i = 1, 2,..., N) of each dye as an explanatory variable. A regression parameter a _i (i = 1, 2,..., N) of the absorbance spectrum of the skin of the subject is obtained, and this regression parameter a _i (i = 1, 2,..., N) and the above-described relation F _i (i = 1, 2,..., N), and at least one of a plurality of pigment concentrations C _i (i = 1, 2,..., N) of the skin of the subject is determined.   The skin pigment concentration measuring method according to claim 1, wherein a skin Monte Carlo simulation is used as a simulation model of skin pigment concentration and spectral reflectance.   The skin pigment concentration measuring method according to claim 1 or 2, wherein an absorbance spectrum of the subject's skin is obtained from an internal reflection image of the subject's skin. The skin pigment concentration measuring method according to any one of claims 1 to 3, wherein at least one pigment concentration of a melanin concentration _Cm , an oxidized hemoglobin concentration _Coh , and a reduced hemoglobin concentration _Cdh is obtained.   The formation of a skin pigment image for determining at least one pigment concentration of the skin by the method according to any one of claims 1 to 3 and forming a distribution image of the pigment concentration for each pixel of the internally reflected light image of the subject's skin Method. 6. The method of forming a skin pigment image according to claim 5, wherein a distribution image of at least one pigment concentration of melanin concentration C _m , oxidized hemoglobin concentration C _oh , and reduced hemoglobin concentration C _dh is formed.   A skin pigment image formed by the method according to claim 5 or 6.