KR20180131082A - System and Method for measuring thickness of cosmetics - Google Patents

Abstract

An apparatus for measuring thickness of a cosmetic material according to an embodiment of the present invention includes an extinction coefficient calculating unit for calculating an extinction coefficient of a test cosmetic, An inner reflected light measuring unit for measuring the intensity of the inner reflected light before applying the test cosmetic and the intensity of the inner reflected light after applying the test cosmetic to the target skin, And a thickness calculating section for calculating the thickness of the test cosmetics according to the Lambert law on the basis of the intensity.

Description

TECHNICAL FIELD [0001] The present invention relates to a thickness measuring device,

The present invention relates to an apparatus and a method for measuring the thickness of a cosmetic material, and an apparatus and a method for measuring the thickness of a cosmetic material applied to the skin.

The purpose of skin make-up is to make it look beautiful and healthy skin. Skin make-up products generally have a covering ability to cover dirt such as dots and pigmentation of the skin, but consideration should be given not only to the efficacy of the cosmetic but also to the senses of use.

Specifically, if the makeup product is to be thickly applied to express the desired coverage, the user will evaluate " thickened. &Quot; Conversely, if the makeup product is thin enough to represent the desired coverage, the user will evaluate it as "feather-like" or "thinly-beaten".

Accordingly, various studies for measuring the thickness of cosmetic materials have been conducted.

Specifically, there is a method of analyzing based on color difference of an image. In this case, a method of evaluating the make-up thickness by applying the Kubelka-Munk theory based on the skin color change value after photographing the image before and after the application of the cosmetic material was proposed. In this case, there is a problem that only the thickness of the relative cosmetic material can be known, and the absolute thickness of the cosmetic material can not be measured.

In addition, there is a method of measuring the thickness of a cosmetic material using the skin texture height information by using a fringe projection. In this case, the thickness of the cosmetic composition is calculated using the difference in average height between the application site of the cosmetic composition and the non-cancellation site using the skin texture height information. However, in this case, because the skin texture should be measured at a certain place, there is a disadvantage that the skin can be measured only in a flat and hard area.

JP 3798550 B2

An object of the present invention is to provide an apparatus and a method for measuring thickness of a cosmetic material which can measure an absolute thickness of a cosmetic material and can easily be measured at any place in consideration of bending skin characteristics.

An object of the present invention is to provide an apparatus and a method for measuring the thickness of a cosmetic material which can precisely measure the thickness of the cosmetic material using reflected light inside the skin.

An apparatus for measuring thickness of a cosmetic material according to an embodiment of the present invention includes an extinction coefficient calculating unit for calculating an extinction coefficient of a test cosmetic, An internal reflection light measuring unit for measuring the intensity of the internal reflected light and the intensity of the internal reflected light after applying the test cosmetics to the target skin, and a controller for calculating, based on the calculated extinction coefficient and the intensity of the reflected light before and after applying the test cosmetics And a thickness calculating section for calculating the thickness of the test cosmetic material according to the Lambert law.

Wherein the thickness calculating unit calculates the thickness of the test cosmetics before and after applying the test cosmetics to the target skin by measuring the extinction coefficient α _t of the test cosmetics measured by the extinction coefficient measuring unit and the first light intensity The thickness d _t of the test cosmetic material can be calculated according to the following formula 2 on the basis of I ₀ and the second light intensity I _t of the internal reflected light after the test cosmetic is applied to the target skin.

[Formula 2]

I _t = I ₀ exp (-α _t × d _t )

Wherein the extinction coefficient calculating unit comprises a plate on which the test cosmetic is applied, a first light source for irradiating light onto the plate, a first optical sensor for measuring transmitted light passing through the plate or the plate to which the test cosmetic is applied, And an extinction coefficient output unit for outputting an extinction coefficient of the test cosmetic based on a ratio of a third light intensity passing through the plate and a fourth light intensity passing through the plate and the test cosmetic.

Wherein the inside reflected light measuring unit includes a light shielding unit that divides a first area where light is irradiated and a second area that measures internally reflected light in the target skin, Two light sources, and a second photosensor that measures light reflected on the second area.

A method for measuring thickness of a cosmetic material according to an embodiment of the present invention includes the steps of calculating an extinction coefficient of a test cosmetic material, calculating an intensity of an internal reflected light before applying the test cosmetic material to a target skin, And calculating the thickness of the test cosmetics according to the Lambert law based on the calculated extinction coefficient and the intensity of the reflected light before and after applying the test cosmetics .

The method according to any one of claims 1 to 3, wherein in the step of calculating the thickness, the extinction coefficient? _T of the test cosmetic, the first light intensity I ₀ of the internal reflected light before applying the test cosmetic to the target skin, It is possible to calculate the thickness d _t of the test cosmetic according to the following formula 2 on the basis of the second light intensity I _t of the internal reflected light after the test.

[Formula 2]

I _t = I ₀ exp (-α _t × d _t )

Calculating the extinction coefficient comprises measuring a third light intensity I ₃ of light passing through the plate, applying the test cosmetic material having a predetermined thickness d ₀ to the plate, measuring the light intensity of the light passing through the plate and the test cosmetic The fourth light intensity I ₄ is measured, and the extinction coefficient α _t of the test cosmetic material can be outputted according to the following formula 3.

[Formula 3]

I ₄ = I ₃ exp (-α _t × d _o )

The step of measuring the internally reflected light may include dividing the target skin into a first zone and a second zone adjacent to the first zone, irradiating the first zone with light, measuring a first optical intensity reflected from the second zone, , Applying the test cosmetics to the second zone, and injecting light into the first zone to measure the second optical intensity reflected from the second zone.

And calculating a light intensity corresponding to a distance from the light source in the first zone and the second zone and calculating a light intensity before or after application of the test cosmetic in a second zone within a predetermined range in a first zone corresponding to the second zone The first light intensity I ₀ or the second light intensity I _t can be calculated through summing.

According to one embodiment of the present invention, it is possible to provide an apparatus and method for measuring thickness of a cosmetic material, which can measure an absolute thickness of a cosmetic material, and can easily be measured at any place in consideration of curved skin characteristics.

According to an embodiment of the present invention, there can be provided an apparatus and method for measuring thickness of a cosmetic material, which can precisely measure the thickness of the cosmetic material using reflected light inside the skin.

1 is a view schematically showing a reflection structure of the skin.
2 is a view schematically showing an apparatus for measuring thickness of a cosmetic material according to an embodiment of the present invention.
3 is a view schematically showing an extinction coefficient measuring unit according to an embodiment of the present invention.
4 is a view schematically showing an internal reflected light measuring unit according to an embodiment of the present invention.
FIG. 5 is a graph illustrating light intensities of internally reflected light according to the distance of skin measured according to an embodiment of the present invention.
FIG. 6 is a graph showing the graphs of FIG.
7 is a view schematically showing a method of measuring the thickness of a cosmetic material according to an embodiment of the present invention.
8 is a view showing a method of measuring the thickness of a cosmetic material according to an embodiment of the present invention.

These embodiments are capable of various modifications and various embodiments, and specific embodiments will be described in detail with reference to the drawings. It is to be understood, however, that it is not intended to limit the scope of the specific embodiments but includes all transformations, equivalents, and alternatives falling within the spirit and scope of the disclosure disclosed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of the embodiments of the present invention,

In the embodiment, 'module' or 'sub' performs at least one function or operation, and may be implemented in hardware or software, or a combination of hardware and software. In addition, a plurality of 'modules' or a plurality of 'parts' may be integrated into at least one module except for 'module' or 'module' which need to be implemented by specific hardware, and implemented by at least one processor (not shown) .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Referring to the accompanying drawings, the same or corresponding elements are denoted by the same reference numerals, and a duplicate description thereof will be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram schematically showing an optical model of the skin. Fig. Figure 1 shows the path of the light incident on the skin (3, 4). Part of the incident light is reflected on the surface of the skin (3). Some are absorbed by the epidermis (3) and the dermis (4), while the rest are reflected by the epidermis (3) and the dermis (4)

The Lambert's law is a law indicating the relationship between the intensity of incident light and the intensity of transmitted light in an absorptive medium. The intensity of incident light is represented by I _{incident light} The intensity of the transmitted light or the emitted light is represented by I _{outgoing light} , It can be expressed as [Expression 1] as follows.

[Formula 1]

I _{outgoing light} = I _{incident light} exp (-α × d)

Where alpha is the absorption coefficient of the medium and d is the thickness of the medium.

The present invention relates to a device for measuring thickness of a cosmetic material which can measure the thickness of a cosmetic material to be tested by measuring the intensity of light incident through the cosmetic material and the intensity of light passing through the cosmetic material by using the internally reflected light reflected from the inside of the skin system and thickness measurement method.

2 is a view schematically showing an apparatus for measuring thickness of a cosmetic material according to an embodiment of the present invention.

An apparatus for measuring thickness of a cosmetic material according to an embodiment of the present invention includes an extinction coefficient calculating unit 10 for calculating an extinction coefficient of a test cosmetic, An internal reflected light measuring unit 20 for measuring the intensity of the internal reflected light after applying the test cosmetics to the test cosmetics, and a thickness calculating unit 30 for calculating the thickness of the test cosmetics according to the Lambert law.

3 is a view schematically showing an extinction coefficient calculating unit 10 according to an embodiment of the present invention.

In order to apply the Lambert's law, the extinction coefficient of the cosmetic should be calculated. If the extinction coefficient is known in advance, the extinction coefficient calculating unit 10 may use a known or calculated extinction coefficient.

However, if the extinction coefficient of the test cosmetic material is not known, a configuration such as that shown in Fig. 3 can be used to measure it.

Specifically, the extinction coefficient calculating unit 10 includes a plate 12 to which the test cosmetic is applied, a first light source 11 that irradiates light onto the plate 12, a plate 12, A first light sensor 13 for measuring the transmitted light passing through the plate 12 to which the cosmetic is applied and a third light intensity I ₃ passing through the plate 12 and the plate 12 and the test cosmetic And an extinction coefficient output unit 15 for outputting the extinction coefficient? _T of the test cosmetic based on the fourth light intensity I ₄ .

As the plate 12, for example, a slide glass may be used. And a test cosmetics X having a predetermined thickness d _o are applied on the plate 12. [ The plate 12 is flat and facilitates the application of the test cosmetic X having a desired thickness and has a high light transmittance so that the difference in light intensity before and after application of the test cosmetic X can be easily measured ≪ / RTI >

The first light source 11 irradiates light onto the plate 12 and the first sensor 13 transmits light transmitted through the plate 12 or the test cosmetic X and the plate 12, of claim (see (a) in Fig. 3) three light intensity I ₃ or 4 can be configured to measure the light intensity I ₄ (see (b) in Fig. 3). The first light source 11 and the first photosensor 13 can be applied to various known members that can irradiate light onto the plate 12 and measure the light intensity of the transmitted light.

3 (a)) of the transmitted light having passed through only the plate 12 and the third light intensity I ₃ (see FIG. 3 (a)) of the plate 12 to measure the extinction coefficient of the test cosmetic X, And the fourth light intensity I ₄ (see FIG. 3 (b)) of the test cosmetics X applied with the predetermined thickness d ₀ .

The extinction coefficient output unit 15 calculates the following equation 3 based on the thickness d ₀ of the test cosmetics X, the third light intensity I ₃ and the fourth light intensity I ₄ , and according to the Lambert law It is possible to output the extinction coefficient alpha _t .

[Formula 3]

I ₄ = I ₃ exp (-α _t × d _o )

Since the values of d ₀ , I ₃ and I ₄ are known, the extinction coefficient α _t of the test cosmetic material X can be outputted through the above equation.

4 is a view schematically showing an internal reflected light measuring unit 20 and a thickness calculating unit 30 according to an embodiment of the present invention.

In order to measure the thickness of the cosmetic material applied on the skin, the transmitted light of the test cosmetic material X should be measured as in the above-described absorption coefficient calculation unit 10 described above. That is, it is necessary to know the light intensity of the transmitted light before the test cosmetic X is applied on the skin and the light intensity of the transmitted light after the test cosmetic X is applied on the skin. Based on the Lambert law described above, ) Can be measured.

That is, in the case of the extinction coefficient calculating unit 10, since the plate 12 is in the shape of a flat plate, any one of the light source and the optical sensor may be disposed on one side of the plate 12, And the transmitted light was measured.

However, if any one of the light source or the light sensor is disposed on one side of the target skin (Y), the other should be placed in the target skin (Y). However, it is not easy to dispose a light source or an optical sensor in the target skin Y. [

Therefore, in the case of the present invention, the difference between the transmitted light passing through the cosmetic material and the target skin is measured through the reflected light of the inside of the target skin (Y).

4, the internal reflected light measurement unit 20 includes a first zone A _{1 in} which light is irradiated and a second zone A _{2 in} which internally reflected light is measured in the target skin. A second light source 21 for emitting light on the first zone A ₁ and a second light sensor 21 for measuring light reflected on the second zone A ₂ , 23).

As described in FIG. 1, since the light reflected from the inside of the skin reflects out of the skin due to the reflection of the substance in the skin, the reflected light is reflected by the skin, It is possible to measure the light intensity which is reflected by the test cosmetic material (X) to the outside.

Referring again to FIG. 4, the first zone A ₁ is a zone for irradiating light onto the target skin Y. FIG. The second zone A ₂ is a zone to which the test cosmetics X is applied and for measuring the difference in light intensity of the internally reflected light.

The first region (A ₁₎ there is a second light source 21 disposed on, since but the light is incident to measure the difference of the internal reflection light coming out through the test cosmetic composition (X), the first region (A ₁ ), The test cosmetic X is not applied.

The second section (A ₂₎ is to be disposed a shielding part 25 to the second to remove the influence due to the surface reflection by the light source 21 in the first region (A ₁₎ in order to measure only the internal reflection light And the second light source 21 can be disposed in the light-shielding portion 25.

4 (a)) and after application (Fig. 4 (b)) of the test cosmetic X by arranging the second photosensor 23 on the second zone A ₂ , Can be measured.

FIG. 5 is a graph illustrating light intensities of internally reflected light according to distances from a light source of an image of the skin, measured according to an embodiment of the present invention.

When light is irradiated onto one spot of the first zone A ₁ , light enters the skin and diffuses inside the skin, and is measured through the second photosensor 23 in the second zone A ₂ do. The second light sensor 23 corresponds to the light source, that is, the distance from the light irradiation spot on the skin, so that a graph of the light intensity according to the distance from the light source as shown in FIG. 5 can be obtained.

5 (a) shows the light intensity according to the distance when the cosmetic is not applied, (b) shows the light intensity according to the distance when the test cosmetic of the first thickness is applied, Of light intensity according to the distance when the test cosmetic is applied.

Of Figure 5 (a), (b) and (c) a period corresponding to a, A1 'in each graph, it is the light blocked by the light shield 25. With reference is the first region (A ₁₎ , And the second zone A ₂ starts from a section corresponding to A2 'in which the internal reflected light abruptly increases.

Referring to FIG. 6, a change in light intensity on the second zone A ₂ can be compared through a starting point correction in the light intensity graph according to distance.

It can be seen that the light intensity is decreased before and after the application of the test cosmetic X and after the application of the test cosmetics of the first and second thicknesses different from each other, the reduction of the light intensity is also distinguished.

5 and 6, the through the graph or data, calculating a first interval (A ₂ ') corresponding to the second section (A ₂₎ to which the test cosmetic coating, and the first section (A ₂ ') Through the sum of the light intensities before and after application of the test cosmetics in a second section (A ₃ ) of a predetermined range (corresponding to T ₁ to T ₂ in the graph of FIG. 5) ₀ and the second light intensity I _t can be calculated, respectively.

The thickness of the test cosmetic X can be calculated through the sum of the light intensities in the corresponding second section A ₃ in each light intensity data.

The thickness calculating unit 30 is connected to the internal reflected light measuring unit 20 and the extinction coefficient calculating unit 10 to calculate the thickness of the test cosmetics X applied on the target skin Y based on the Lambert law d _t can be calculated.

Specifically, the first light intensity I ₀ before application and the second light intensity I _t after application are measured by the internal reflected light measurement unit 20, and using the extinction coefficient α _t of the test cosmetics X identified above, The thickness d _t of the test cosmetic material X applied on the target skin Y can be calculated according to the following formula 2 based on the law of Berth.

[Formula 2]

I _t = I ₀ exp (-α _t × d _t )

7 is a view schematically showing a method of measuring the thickness of a cosmetic material according to an embodiment of the present invention.

A method for measuring thickness of a cosmetic material according to an embodiment of the present invention includes the steps of calculating an extinction coefficient of a test cosmetic material (S10), calculating an intensity of an internal reflected light before applying the test cosmetic material to a target skin, A step S20 of measuring the intensity of the internal reflected light after applying the cosmetic, and a step S30 of calculating the thickness of the test cosmetic according to the Lambert law.

The method for measuring the thickness of a cosmetic material according to the present invention relates to a method for measuring the thickness of a cosmetic material by the above-described apparatus for measuring thickness of a cosmetic material, and the content of the thickness measuring apparatus described above is applied thereto. In the opposite case, that is, the method of measuring the thickness of the cosmetic material is also applied to the thickness measuring apparatus.

In the step (S10) of calculating the extinction coefficient, it is possible to calculate the extinction coefficient by measuring the extinction coefficient of the test cosmetics (X) It is possible.

Then, in the step (S20) of measuring the intensity of the internal reflected light measuring a first light intensity I ₀ of the inner reflected light prior to application of the test cosmetic composition (X) to the target skin, and applying a test cosmetic composition (X) to the target skin It is possible to measure the second light intensity I _t of the internally reflected light after it has been measured.

Although the step of calculating the extinction coefficient (S10) is first described in the step of calculating the extinction coefficient (S10) and the step of measuring the intensity of the internally reflected light (S20), this step is not limited to the order. The calculating step S10 may be performed first, and the step S20 of measuring the intensity of the internally reflected light may be performed first. However, it may be used before the step S30 of calculating the thickness of the cosmetic material, and the intensity of the extinction coefficient and the intensity of the internally reflected light may be used in the step S30 of calculating the thickness.

Then, the of the first light intensity I ₀ measured at the step (S20) and the absorption coefficient α _t of the test cosmetic composition (X) calculated in the step (S10) of calculating the extinction coefficient, which measures the intensity of the internal reflected light, the The thickness d _t of the test cosmetic material can be calculated by the Lambert law in the step S30 of calculating the thickness of the test cosmetic material X based on the two light intensities I _t .

8 is a view showing a method of measuring the thickness of a cosmetic material according to an embodiment of the present invention.

Specifically, in the step (S31) of calculating the thickness, the extinction coefficient? _T of the test cosmetic, the first light intensity I ₀ of the internally reflected light before applying the test cosmetic to the target skin, The thickness d _t of the test cosmetic material can be calculated in accordance with the following formula 2 based on the second light intensity I _t of the internal reflected light after application of the test cosmetic material.

[Formula 2]

I _t = I ₀ exp (-α _t × d _t )

More specifically, when the extinction coefficient of the test cosmetic material X is unknown, the step of measuring the extinction coefficient S 10 is performed by measuring a third light intensity I ₃ of light passing through the plate (S 11) Applying the test cosmetic material having a predetermined thickness d ₀ and measuring a fourth light intensity I ₄ of the light passing through the plate and the test cosmetic material (S13), and calculating an extinction coefficient of the test cosmetic material according to the following formula (3) (? _t ) (S15).

[Formula 3]

I ₄ = I ₃ exp (-α _t × d _o )

In addition, the step (S20) of measuring the internally reflected light may be performed by dividing the target skin into a first zone and a second zone adjacent to the first zone, irradiating light to the first zone, first measuring the light intensity I ₀ and (S21), applying the test cosmetic composition in the second zone, measuring a second light intensity I _t to incident light from being reflected by the second zone to the first zone (S23).

In order to measure the thickness of the test cosmetics not knowing the extinction coefficient, the extinction coefficient was first calculated.

The light intensity of the transmitted light of the slide glass to which nothing was applied was measured, and the test cosmetics were applied to a slide glass of 100 mu m, and then the light intensity of the transmitted light was measured. This was measured three times and the average of them was measured. The results are shown in Table 1 below.

Light intensity 1  Light intensity 2 Light intensity 3 Average Slide glass 60240 60614 60224 60359 Slide glass
+ Test cosmetic 358 358 358 358

The average value was substituted for the Lambert's formula, and as a result, the extinction coefficient of the test cosmetic was 0.0513 / 탆.

Then, the thickness of the same test cosmetics applied at different thicknesses was measured. That is, after application of the test cosmetic material to the first and second thicknesses, which were different from each other, the light source was incident on the first zone and the light intensity was measured in the second zone, as shown in the graph of FIG. In the case of the second thickness, a large amount of about 8 times as much as the first thickness was applied, and the first thickness was applied to a thin thickness and the second thickness to a thick thickness.

That is, the light intensity of the internally reflected light according to the distance from the light source measured in the state where the test cosmetic material was not coated was the same as the graph (a) of FIG. 5, The light intensity was the same as the graph (b), and the light intensity of the internally reflected light according to the distance from the light source in the state of being coated with the second thickness was the same as the graph (c).

The raw data of the light intensity according to the distance from the light source, that is, the light irradiation spot, was calculated, and the first and second regions were confirmed. The graph showing the correction of the starting point of only the second zone was as shown in Fig.

The light intensity values were calculated as follows through the sum of light intensities within a predetermined section (a section ranging from 26 pixels to 100 pixels) in the second zone.

- First light intensity without test cosmetic applied: 7692

Second light intensity when the test cosmetic is applied to the first thickness: 6408

- Second light intensity when the test cosmetic is applied to the second thickness: 2069

As a result, since the extinction coefficient was 0.0513 / 탆, the first thickness d ₁ and the second thickness d ₂ could be calculated by applying the Lambert's law equation as follows.

- first thickness (d ₁ ) = 3.56 탆

- second thickness (d ₂ ) = 25.60 탆

In the case of the second thickness, the coating amount was about 8 times larger than the first thickness, and these results were confirmed in the measurement results.

10: Extinction coefficient calculation unit
11: First light source
12: Plate
13: first optical sensor
15: extinction coefficient output section
20:
21: second light source
23: second optical sensor
25:
30: Thickness calculating section of cosmetic material

Claims (9)

An extinction coefficient calculating unit for calculating an extinction coefficient of the test cosmetic;
An internal reflected light measuring unit for measuring the intensity of the internal reflected light before applying the test cosmetic to the target skin and the intensity of the internal reflected light after applying the test cosmetic to the target skin; And
And a thickness calculating section for calculating the thickness of the test cosmetic material in accordance with the Lambert law, based on the calculated extinction coefficient and the intensity of the internal reflected light before and after applying the test cosmetic material.
The method according to claim 1,
The thickness calculating unit may calculate,
An extinction coefficient? _T of the test cosmetic material measured by the extinction coefficient measuring unit,
The first light intensity I ₀ of the internal reflected light before coating the test cosmetics on the target skin measured by the internal reflected light measuring unit and the second light intensity I ₀ of the internal reflected light after coating the test cosmetics on the target skin Based on _t ,
And the thickness d _t of the test cosmetic material is calculated according to the following formula (2).
[Formula 2]
I _t = I ₀ exp (-α _t × d _t )
The method according to claim 1,
Wherein the extinction coefficient calculating unit comprises:
A plate to which the test cosmetic is applied;
A first light source for irradiating light onto the plate;
A first photosensor for measuring transmitted light passing through the plate or the plate to which the test cosmetic is applied; And
And an extinction coefficient output unit for outputting an extinction coefficient of the test cosmetic based on a ratio of a third light intensity passing through the plate and a fourth light intensity passing through the plate and the test cosmetic material, Measuring device.
The method according to claim 1,
Wherein the internal reflected light measuring unit comprises:
A light shielding part for separating a first area irradiated with light and a second area measuring internally reflected light in the target skin;
A second light source, disposed in the light-shielding portion, for illuminating the first region; And
And a second photosensor for measuring the light reflected on the second area.
Calculating an extinction coefficient of the test cosmetic;
Measuring the intensity of the internal reflected light before applying the test cosmetic to the target skin and the intensity of the internal reflected light after applying the test cosmetic to the target skin; And
And calculating the thickness of the test cosmetic according to the Lambert law, based on the calculated extinction coefficient and the intensity of the internal reflected light before and after applying the test cosmetic.
6. The method of claim 5,
In the step of calculating the thickness,
The extinction coefficient? _T of the test cosmetic,
On the basis of the first light intensity I ₀ of the internal reflected light before applying the test cosmetic to the target skin and the second light intensity I _t of the internal reflected light after applying the test cosmetic to the target skin,
The thickness d _t of the test cosmetic material is calculated according to the following formula (2).
[Formula 2]
I _t = I ₀ exp (-α _t × d _t )
6. The method of claim 5,
The step of calculating the extinction coefficient comprises:
Measuring a third light intensity I ₃ of light passing through the plate,
Applying the test cosmetic material having a predetermined thickness d ₀ to the plate and measuring a fourth light intensity I ₄ of the light passing through the plate and the test cosmetic material,
Wherein the extinction coefficient? _T of the test cosmetic is output according to the following formula (3).
[Formula 3]
I ₄ = I ₃ exp (-α _t × d _o )
6. The method of claim 5,
Wherein the step of measuring the internal reflected light comprises:
Dividing the target skin into a first zone and a second zone adjacent thereto, introducing light into the first zone, measuring a first light intensity reflected by the second zone,
Applying the test cosmetics to the second zone, and injecting light into the first zone to measure a second light intensity reflected from the second zone.
9. The method of claim 8,
And calculating a light intensity corresponding to a distance from the light source in the first zone and the second zone and calculating a light intensity before or after application of the test cosmetic in a second zone within a predetermined range in a first zone corresponding to the second zone Wherein the first light intensity I ₀ or the second light intensity I _t is calculated through summing.

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