WO2024070753A1

WO2024070753A1 - Skin evaluation method, skin evaluation device, and program

Info

Publication number: WO2024070753A1
Application number: PCT/JP2023/033654
Authority: WO
Inventors: 久美子菊地; 佳永相津; 友典湯浅
Original assignee: 株式会社資生堂
Priority date: 2022-09-30
Filing date: 2023-09-15
Publication date: 2024-04-04

Abstract

This skin evaluation method includes acquiring information about emission light emitted from the interior of the skin irradiated with light, and evaluating the state of the skin at a prescribed depth using information about light having a prescribed wavelength from among the emission light emitted from the skin interior.

Description

SKIN EVALUATION METHOD, SKIN EVALUATION DEVICE, AND PROGRAM

The present invention relates to a skin evaluation method, a skin evaluation device, and a program.

A method of evaluating skin that uses information on light reflected from shining light on the skin is known. For example, Patent Document 1 describes a method of evaluating skin condition using skin image data corresponding to an evaluation target area of the skin, which is obtained by projecting linear or dot-like light onto the skin of a subject and receiving light reflected on the surface and inside the skin, in which skin image data consisting of a collection of images of the skin area a predetermined distance away from the projection position of the light on the skin is obtained, and the skin condition of the evaluation target area is evaluated based on each spatial distribution of reflected light on the skin surface and inside the skin indicated by the distribution value of the reflected light intensity for each predetermined distance calculated from the skin image data. The skin condition evaluated by the method described in Patent Document 1 is specifically the transparency of the skin, which is the external impression or the beauty of the skin as visually recognized by a person.

Patent No. 6029379

In recent years, there has been a demand for more detailed evaluation of skin conditions. For this reason, for example, it is important to analyze and evaluate the condition of skin tissue. However, such analysis of skin tissue condition often requires large-scale equipment using precision instruments, which can be a burden for subjects.

In view of the above, one aspect of the present invention aims to provide a simple method for evaluating skin condition in more detail.

In order to solve the above problems, a skin evaluation method according to one aspect of the present invention involves acquiring information on light emitted from inside the skin irradiated with light, and evaluating the condition of the skin at a predetermined depth using information on light of a predetermined wavelength among the light emitted from inside the skin.

One aspect of the present invention provides a simple method for evaluating skin conditions in more detail.

FIG. 1 is a diagram for explaining skin structure (skin tissue). 1 is a flowchart of a skin evaluation method according to an embodiment. 11A and 11B are diagrams for explaining acquisition of image data of light emitted from inside the skin. 4 shows examples of acquired image data and spectroscopic image data. 1 is an overall configuration diagram according to an embodiment of the present invention; 1 is a functional block diagram of a skin evaluation device according to an embodiment of the present invention. 1 is a block diagram showing an example of a hardware configuration of a skin evaluation device according to an embodiment of the present invention. FIG. 11 is a diagram showing the relationship between the melanin index and the amount of melanin obtained in an application example of the first embodiment. FIG. 13 is a diagram showing the relationship between the hemoglobin index and the hemoglobin amount obtained in an application example of the third embodiment. FIG. 13 is a diagram showing the relationship between collagen volume density index and collagen volume density obtained in an application example of the third embodiment. FIG. 13 is a diagram showing the relationship between age and stratum corneum level obtained in an application example of the fourth embodiment. FIG. 11 is a diagram summarizing the results of an example of comprehensive skin evaluation using multiple skin evaluation methods according to the present embodiment.

<Skin evaluation method>
A skin evaluation method according to an embodiment of the present invention obtains information on light emitted from inside the skin irradiated with light, and evaluates the condition of the skin at a predetermined depth by using information on light of a predetermined wavelength among the light emitted from inside the skin. The evaluation obtained by this embodiment is an evaluation for cosmetic purposes. In addition, in this specification, the "light of a predetermined wavelength" may be light having a single wavelength, or light having a predetermined wavelength range (wavelength width). It may also be light obtained by synthesizing light having two or more different predetermined single wavelengths, or light obtained by synthesizing light having two or more different predetermined wavelength ranges.

When light is irradiated onto the skin, the irradiated light exhibits various behaviors due to the translucency of the skin. For example, the irradiated light can be light reflected from the skin surface in the direction opposite to the direction of irradiation (called "surface reflected light" or "specular reflected light"), light reflected from the skin surface in various directions other than the direction of irradiation due to the unevenness of the skin surface (also called "diffuse reflected light" or "surface diffuse reflected light"), light absorbed inside the skin (below the skin surface), or light scattered inside the skin (below the skin surface) and emitted to the outside from the skin surface. Of these types of light, light scattered inside the skin and emitted to the outside from the skin surface is called "subsurface scattered light", "internal scattered light", "internal reflected light", "internal diffuse light", "diffuse light", "internal propagating light", "intraskin light", etc., but in this specification it is called "light emitted from inside the skin" or "light emitted from inside". Note that even if light enters the skin and is scattered inside the skin, light that does not exit from the skin surface is considered to be light absorbed by the skin and is not included in "light emitted from inside the skin". In addition, in this specification, "surface reflected light" and "diffusely reflected light" are collectively referred to as "light reflected from the skin surface," and this "light reflected from the skin surface" and "light emitted from inside the skin" are collectively referred to as "total returned light."

This embodiment is a method for evaluating skin that utilizes information about the light emitted from inside the skin. The inventors have found that the penetration depth within skin tissue varies depending on the wavelength of light emitted from inside the skin, and further that the state of skin tissue at a given depth in the skin is reflected in information about light emitted from inside the skin at a given wavelength. The present invention is based on this knowledge. Here, the state of skin at a given depth refers to the state at a given position in the skin tissue, or the state of a given layer in the skin tissue. Furthermore, the light information includes image data.

Skin tissue has a structure consisting of multiple layers, each of which has a specific structure or composition, properties, and functions. In this embodiment, the condition of one or more of the layers that make up the skin tissue can be evaluated. Figure 1 shows a schematic diagram of skin tissue (skin structure). As shown in Figure 1, the skin is roughly divided into the epidermis, dermis, and subcutaneous tissue, in order from the skin surface. In this model, the epidermis includes the stratum corneum, which is the most superficial layer, the granular layer and spinous layer (granular layer and/or spinous layer) that follow below, and the basal layer (basement membrane). The dermis includes, in order from the skin surface, the papillary layer, the subpapillary layer, the upper capillary plexus layer, the reticular layer, and the lower capillary plexus layer. Below the lower capillary plexus layer is the subcutaneous tissue. Therefore, in this embodiment, for example, the condition of one or more of the epidermis and dermis can be evaluated, or in more detail, the condition of one or more layers included in the epidermis and/or one or more layers included in the dermis can be evaluated.

The inventors have found that information on blue and/or green light from the light emitted from inside the skin irradiated with light is highly related to the state of the epidermis in the skin tissue. An evaluation method according to one embodiment based on this finding includes evaluating the state of the epidermis using information on blue and/or green light from the light emitted from inside the skin. In particular, since information on blue light from the light emitted from inside the skin irradiated with light is highly related to the state of the granular layer and/or the spinous layer of the epidermis, a skin evaluation method according to one embodiment of the present invention includes evaluating the state of the granular layer and/or the spinous layer using information on blue light from the light emitted from inside the skin. In addition, since information on green light from the light emitted from inside the skin irradiated with light is highly related to the state of the basal layer of the epidermis, a skin evaluation method according to one embodiment of the present invention includes evaluating the state of the basal layer using information on green light from the light emitted from inside the skin.

In one embodiment of the skin evaluation method, information on the total return light from the skin irradiated with light (light information including information on reflected light from the skin surface and information on light emitted from within the skin) can also be obtained, and the total return light information and information on light of a predetermined wavelength among the light emitted from within the skin can be used. For example, the state of the stratum corneum can be evaluated using information on blue light among the total return light and information on blue light among the light emitted from within the skin. In this case, the difference between the information on blue light among the total return light and the information on blue light among the light emitted from within the skin is used.

Furthermore, the inventors have found that red light information from the light emitted from inside the skin irradiated with light is highly related to the state of the dermis in the skin tissue. One form of evaluation method based on this finding involves evaluating the state of the dermis using red light information from the light emitted from inside the skin. Furthermore, in evaluating the state of the dermis, in addition to the red light information from the light emitted from inside the skin, green light information from the light emitted from inside the skin can also be used. In this case, the difference between the red light information from the light emitted from inside the skin and the green light information from the light emitted from inside the skin can be used.

Conventional methods for analyzing and evaluating the condition of skin tissue include photoacoustic microscopy, confocal microscopy, multiphoton microscopy, and optical coherence tomography (OCT), but these methods require large-scale equipment and are not easily accessible because the measurements are time-consuming and laborious. In contrast, this method uses information on the light emitted from within the skin when light is irradiated, and the information on the light emitted from within, which is necessary for evaluation, can be obtained using imaging equipment, etc., making it easier to perform detailed evaluation of the skin compared to conventional technologies.

FIG. 2 shows a flow chart of a specific example of the evaluation method according to this embodiment. As shown in FIG. 2, more specifically, the evaluation method according to this embodiment may include a step of irradiating light onto the subject's skin (S1), a step of separating image data of light emitted from inside the skin from image data of all returned light (S2), a step of generating spectral image data of a predetermined wavelength from the image data (S3), a step of calculating an index using the image data (S4), and a step of evaluating the state of a predetermined layer in the skin tissue based on the index (S5).

The light source used in the light irradiation step (S1) is preferably a light source capable of irradiating light including visible light, for example a white light source. A white light source has a wide continuous wavelength range including the wavelength of visible light, so it is possible to obtain information for evaluating the state at various depth positions in the skin tissue or the state of various layers in the skin tissue. If the specific layer to be evaluated in the skin tissue (the depth position to be evaluated in the skin tissue) is predetermined, the light source only needs to include a specific wavelength that reflects the state of the specific layer to be evaluated in the skin tissue (the state at the depth position of the skin tissue). In addition, the light irradiated from the light source is preferably light irradiated in a narrow range in the evaluation target area, for example light that is linear, point-like, or sinusoidal, and a linear or point-like light is particularly preferable in that the calculation is not complicated.

The step (S2) of separating image data of light emitted from inside the skin from image data of all light returned from the skin surface will be described with reference to FIG. 3. In the separation, image data of the skin is acquired (imaged) by an imaging device. The imaging device for acquiring image data can be an RGB camera, a light field camera, a spectral camera, a hyperspectral camera, or the like. When imaging, a pattern including an irradiated area and a non-irradiated area is projected onto the skin area to be evaluated (evaluation target area) (FIG. 3(a)). Such a pattern including an irradiated area and a non-irradiated area can be formed, for example, by projecting an image in which white (= irradiated area) and black (= non-irradiated area) are alternately arranged from a projector, or by placing a stencil in which light-opaque areas and light-transmitting areas are alternately arranged in stripes at the projection port of the projector. As a result, a state in which a pattern including an irradiated area and a non-irradiated area is projected onto the subject's face can be formed, as shown in FIG. 3(a).

Generally, light irradiated onto the area to be evaluated is reflected from the surface of the skin, or passes through the surface of the skin and is scattered inside the skin before exiting from the surface of the skin. Figure 3(b) shows the behavior of light on the skin. Arrow 1 in Figure 3(b) is the irradiated light (light irradiated from the light source to the skin). Arrow 2 is light that is specularly reflected from the irradiated area, and arrow 3 is light that is diffusely reflected from the surface of the irradiated area. Arrow 4 is light that is emitted to the outside of the skin after scattering inside the skin (light that enters the skin, goes around inside the skin, and exits again), in other words, light that is emitted from inside the skin. The light indicated by arrow 5 is light that is absorbed inside the skin and is not emitted to the outside.

The light emitted from the inside is emitted from both the irradiated and non-irradiated areas, but the light emitted from the non-irradiated area is only the light emitted from the inside. Therefore, by measuring the intensity of the light emitted from the non-irradiated area, information on the light emitted from the inside can be obtained locally from the evaluation target area. Then, the above pattern is slid (Fig. 3(c)) so that the non-irradiated area is projected onto the area that was the irradiated area of the evaluation target area, and the light intensity of the light emitted from the inside in the newly projected non-irradiated area is measured. In this way, the intensity of the light emitted from the inside is measured over the entire evaluation target area, and two-dimensional image data of the light emitted from inside the skin can be obtained. Furthermore, by measuring the light intensity of the reflected light in the irradiated area of the evaluation target area, the light intensity of the total return light (i.e., the sum of the light reflected on the skin surface and the light emitted from inside the skin) is also measured over the entire evaluation target area, and two-dimensional image data of the total return light can be obtained. The image size is preferably 20 pixels x 20 pixels or more.

If the above pattern is a striped pattern as shown in the figure, the width of the non-irradiated area may be 0.1 mm or more and 10 mm or less, and the width of the irradiated area may be 0.1 mm or more and 3 mm or less. Furthermore, the pattern does not necessarily have to be striped, and may be a grid pattern or the like as long as the irradiated and non-irradiated areas are repeated on the surface.

In this way, in the image data separation step (S2), when capturing an image, image data of the emitted light from inside the skin can be separated from image data of all returned light, i.e., image data including image data of the reflected light from the skin surface and image data of the emitted light from inside the skin. In other words, image data of the reflected light from the skin surface and image data of the emitted light from inside the skin can be separated from the image data of all returned light. Therefore, in step S2 in this embodiment, one or more of image data of all returned light, image data of the reflected light from the skin surface, and image data of the emitted light from inside the skin can be obtained.

In FIG. 4, an example of image data of light emitted from inside the skin obtained in the separation step (S2) is shown as initial image data Img-0. The initial image data Img-0 includes data on the light intensity of visible light (360-840 nm) in the area to be evaluated. In other words, the initial image data Img-0 is an image represented by the intensity of light emitted from the inside, including visible light.

In the spectral image data generating step (S3), spectral image data of a predetermined wavelength is generated from the image data obtained in the image data separating step (S2). In this spectral image data generating step (S3), spectral image data can be generated from any image data obtained in the image data separating step (S2). More specifically, the spectral image data can be generated from one or more of the image data of the total returned light, the image data of the reflected light on the skin surface, and the image data of the emitted light from inside the skin obtained in the image data separating step (S2). The spectral image data is image data that includes information on light of a predetermined wavelength (information on light intensity). Note that the spectral image data of a predetermined wavelength obtained in the spectral image data generating step (S3) may be spectral image data of a single wavelength, or may be spectral image data of a predetermined wavelength range (wavelength width), or may be spectral image data of light obtained by combining two or more different predetermined single wavelengths of light, or may be spectral image data of light having two or more different predetermined wavelength ranges.

Figure 4 shows an example of generating spectral image data of a specified wavelength from image data of light emitted from inside the skin (initial image data Img-0). Figure 4 is an example of generating spectral image data when an RGB camera is used. As shown in Figure 4, image data Img-B of blue light (wavelength 380-500 nm), image data Img-G of green light (wavelength 500-600 nm), and image data Img-R of red light (wavelength 600-720 nm) can be generated from the initial image data Img-0. Furthermore, by using a spectral camera or hyperspectral camera, it is possible to generate spectral image data of light in any wavelength range. Similarly, spectral image data of a specified wavelength can be generated from the image data of all returned light.

Furthermore, in the index calculation step (S4), an index for skin evaluation is calculated based on at least one of the spectroscopic image data of the above-mentioned predetermined wavelengths. This index may be an index related to the overall magnitude of light intensity, or an index related to distribution. In addition, the index related to the overall magnitude or the index related to distribution may be calculated after converting the light intensity to absorbance by logarithmic transformation. For example, it may be one or more statistics of the average, maximum, minimum, median, integral, sum, standard deviation, variance, skewness, and kurtosis of the light intensity in the evaluation target area.

In addition, in the index calculation step (S4), calculating the index based on the spectroscopic image data includes calculating the index using two or more spectroscopic image data. The two or more spectroscopic image data may be, for example, two spectroscopic image data of light emitted from inside the skin having different predetermined wavelengths, or spectroscopic image data of all returned light having a predetermined wavelength, and spectroscopic image data of light emitted from inside the skin having a predetermined wavelength similar to the predetermined wavelength. Alternatively, it may be spectroscopic image data of all returned light having a predetermined wavelength, and spectroscopic image data of light emitted from inside the skin having a predetermined wavelength different from the predetermined wavelength. When calculating the index using such two or more spectroscopic image data, for example, the index may be calculated after finding the difference, ratio, etc. between the two spectroscopic image data. In that case, differential image data, ratio image data, etc. may be generated, and the index may be calculated based on the differential image data, ratio image data, etc. In other words, calculating the index based on the spectroscopic image data may include calculating the index based on differential image data and ratio image data obtained from two or more spectroscopic image data. An example of differential image data is differential image data obtained by subtracting the spectroscopic image data of light emitted from inside the skin having the same predetermined wavelength from the spectroscopic image data of all returned light having a predetermined wavelength.

The obtained index is used in the step (S5) of evaluating the condition of a specific layer of skin. In order to evaluate the condition of a specific layer of skin, the relationship between the index calculated based on the spectroscopic image data of a specific wavelength and the condition of the specific layer in the skin tissue is obtained in advance and stored as a database. The index calculated based on the spectroscopic image data of a specific wavelength obtained through steps S1 to S4 for the subject whose skin is to be evaluated is applied to such a previously obtained relationship, thereby determining and evaluating the condition of the specific layer in the skin tissue of the subject. Therefore, for example, in the evaluation step (S5), the relationship between the index calculated based on the spectroscopic image data corresponding to the light emitted from inside the skin of a specific wavelength and the condition of the specific layer in the skin tissue is obtained in advance, and the index calculated based on the spectroscopic image data of a specific wavelength obtained through steps S1 to S4 for the subject whose skin is to be evaluated is applied to the relationship, thereby determining and evaluating the condition of the specific layer in the skin tissue. As described above, the spectroscopic image data may include spectroscopic image data generated from the image data of all returned light and spectroscopic image data generated from the image data of light emitted from inside the skin. Furthermore, as described above, when an index is calculated based on difference image data or ratio image data obtained from two or more pieces of spectral image data, the relationship between the index calculated based on such difference image data or ratio image data and the state of a specific layer in the skin tissue is determined in advance, and the index calculated based on difference image data or ratio image data obtained from the spectral image data of a specific wavelength obtained through steps S1 to S4 for the subject whose skin is to be evaluated is applied to this relationship to determine and evaluate the state of the specific layer in the skin tissue.

The condition of a specific layer of the skin evaluated in the evaluation step (S5) may be, for example, the condition of the epidermis or the condition of the dermis. The condition of the epidermis may include one or more of the condition of the stratum corneum, the condition of the granular layer and/or the spinous layer, and the condition of the basement membrane.

<Skin evaluation device>
5 shows a skin evaluation system 1 used in the skin evaluation method according to the present embodiment. As shown in FIG. 5, the skin evaluation system 1 includes a skin evaluation device 10, an imaging device 20, and a light source 30.

The skin evaluation device 10 may be a computer for evaluating the optical characteristics of the skin, and can execute the above-mentioned steps S2 to S5. That is, the skin evaluation device 10 can use the image captured by the imaging device 20 to obtain information on light (emission light from within) that is irradiated from the light source 30, enters the skin, circulates around the skin surface, and is then emitted from the skin surface again. It can also generate spectroscopic image data of a specified wavelength from the image data, and calculate an index for the emission light from within the specified wavelength in the evaluation target area. Furthermore, based on the calculated index, it can use the relationship between the index for the emission light from within the specified wavelength and the state of a specified layer in the skin tissue, which has been previously obtained, to determine and evaluate the state of a specified layer in the skin tissue in the evaluation target area. The skin evaluation device 10 may be a personal computer, a tablet terminal, a smartphone, etc.

The imaging device 20 is a device for photographing skin, and may be an RGB camera, a spectral camera, a hyperspectral camera, a light field camera, etc., as described above. The image captured by such an imaging device 20 is an image expressed by the intensity of internally reflected light, and includes images for each wavelength range obtained by dividing the light emitted from the inside into multiple wavelength ranges.

In the example shown in FIG. 5, the skin evaluation device 10, the imaging device 20, and the light source 30 are described as separate devices, but at least two of the skin evaluation device 10, the imaging device 20, and the light source 30 may be implemented together as a single device. For example, if the imaging device 20 and the skin evaluation device 10 are incorporated into a terminal such as a smartphone, the user can take an image of their own facial skin using the smartphone's built-in camera and evaluate it.

FIG. 6 shows a functional block diagram of the skin evaluation device 10. As shown in FIG. 6, the skin evaluation device 10 may include an image acquisition unit (information acquisition unit) 101, a calculation unit 102, and an evaluation unit 103. The skin evaluation device 10 can function as the image acquisition unit 101, the calculation unit 102, and the evaluation unit 103 by executing a program.

The image acquisition unit 101 acquires from the imaging device 20 an image of the evaluation target area of the skin irradiated with light from the light source 30, which is represented by the intensity of light emitted from inside the skin. From the image acquired from the imaging device 20, the image acquisition unit 101 can acquire information on the light emitted from inside the evaluation target area, more specifically, information on the wavelength or intensity for each wavelength range of the light emitted from inside (for example, each RGB value at each pixel). The image acquisition unit 101 can also generate or extract spectral image data of a predetermined wavelength from the acquired image of light emitted from inside (information on light emitted from inside). Note that the image acquisition unit 101 can also perform some processing, such as noise reduction processing, sharpening processing, correction processing, etc., on the acquired image data or spectral image data.

The calculation unit 102 can calculate an index related to the light emitted from within the specified wavelength or the light emitted from within the specified wavelength range based on the obtained spectroscopic image data of the specified wavelength. The index may be an index related to the overall magnitude of the light intensity, or an index related to the distribution. After converting the light intensity to absorbance, the index related to the overall magnitude or the index related to the distribution may be calculated.

The evaluation unit 103 evaluates the skin based on the index calculated by the calculation unit 102. For example, the evaluation unit 103 can evaluate the state of a specific layer in the skin tissue based on the relationship between an index related to light emitted from within at a specific wavelength, which has been calculated in advance and stored in the skin evaluation device 10, and the state of a specific layer in the skin tissue.

<Hardware Configuration>
FIG. 7 is a block diagram showing an example of a hardware configuration of the skin evaluation device 10 according to an embodiment of the present invention.

The skin evaluation device 10 has a CPU (Central Processing Unit) 1001, a ROM (Read Only Memory) 1002, and a RAM (Random Access Memory) 1003. The CPU 1001, the ROM 1002, and the RAM 1003 form what is known as a computer.

The skin evaluation device 10 may also have an auxiliary storage device 1004, a display device 1005, an operation device 1006, an I/F (Interface) device 1007, and a drive device 1008. Each piece of hardware in the skin evaluation device 10 is connected to each other via a bus B.

The CPU 1001 is a computing device that executes various programs installed in the auxiliary storage device 1004.

ROM 1002 is a non-volatile memory. ROM 1002 functions as a primary storage device that stores various programs, data, etc. required for CPU 1001 to execute various programs installed in auxiliary storage device 1004. Specifically, ROM 1002 functions as a primary storage device that stores boot programs such as BIOS (Basic Input/Output System) and EFI (Extensible Firmware Interface).

RAM 1003 is a volatile memory such as DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory). RAM 1003 functions as a primary storage device that provides a working area into which various programs installed in the auxiliary storage device 1004 are expanded when they are executed by the CPU 1001.

The auxiliary storage device 1004 is an auxiliary storage device that stores various programs and information used when the various programs are executed.

The display device 1005 is a display device that displays the internal state of the skin evaluation device 10, etc.

The operation device 1006 is an input device through which the administrator of the skin evaluation device 10 inputs various instructions to the skin evaluation device 10.

The I/F device 1007 is a communication device that connects to a network and communicates with the skin evaluation device 10.

The drive unit 1008 is a device for setting the storage medium 1009. The storage medium 1009 here includes media that record information optically, electrically, or magnetically, such as CD-ROMs, flexible disks, and magneto-optical disks. The storage medium 1009 may also include semiconductor memory that records information electrically, such as EPROM (Erasable Programmable Read Only Memory) and flash memory.

The various programs to be installed in the auxiliary storage device 1004 are installed, for example, by setting the distributed storage medium 1009 in the drive device 1008 and reading the various programs recorded on the storage medium 1009 by the drive device 1008. Alternatively, the various programs to be installed in the auxiliary storage device 1004 may be installed by downloading them from a network via the I/F device 1007.

The following describes the embodiments of the present invention in more detail.

First Embodiment
The skin evaluation method according to the first embodiment is a skin evaluation method that acquires information on light emitted from inside skin irradiated with light, and evaluates the skin condition in the granular stratum and/or the spinous stratum by utilizing information on blue light from the light emitted from the inside.

Blue light (wavelength 380-500 nm) emitted from inside the skin is mainly reflected by the stratum granulosum and/or stratum spinosum (Figure 1) in the skin tissue and emitted from the skin surface, so the state of the stratum granulosum and/or stratum spinosum can be reflected in image data of the blue light emitted from inside the skin. Therefore, according to this embodiment, for example, the thickness of the epidermis layer, the amount of melanin, etc. can be easily evaluated. For example, by being able to evaluate the amount of melanin, dullness of the skin, uneven skin tone (including age spots, freckles, etc.), sunburn, etc. can be evaluated.

In this embodiment, in the above-mentioned spectral image data generating step (S3) described with reference to Figure 2, blue light spectral image data is generated, and in the index calculation step (S4), an index is calculated using the blue light spectral image data. Therefore, the skin evaluation method according to this embodiment, when explained according to the flow shown in Figure 2, may be a skin evaluation method including a step (S1) of irradiating light to the subject's skin, a step (S2) of separating image data of light emitted from inside the skin from image data of all returned light, a step (S3) of generating blue light spectral image data from image data of light emitted from inside the skin, a step (S4) of calculating an index using the blue light spectral image data, and a step (S5) of evaluating the state of the stratum granulosum and/or stratum spinosum based on the index.

=Application Example (Example) of the First Embodiment=
As an application example of the first embodiment, evaluation of the amount of melanin was studied. Specifically, facial skin images of 24 subjects aged 30 to 39 were taken with an RGB camera. From the obtained image data (image data of all return light), image data of light emitted from inside the skin was separated, and further, spectral image data of blue light (wavelength 380 to 500 nm) was generated from the image data of light emitted from inside the skin, and the light intensity in the spectral image was converted to absorbance, and multiplied by a coefficient determined by multiple regression analysis, which was used as a melanin index (index). Meanwhile, the distribution of the amount of melanin on the entire face of each subject was measured from the spectral spectrum using a spectrophotometer, and the average value was used as the "amount of melanin" of the subject. FIG. 8 shows the relationship between the melanin index and the amount of melanin. As shown in FIG. 8, it was confirmed that there is a high correlation between the two.

Therefore, if the relationship shown in Figure 8 is determined in advance, skin image data is obtained from a subject whose skin melanin amount is to be evaluated, and image data of blue light emitted from inside the skin is generated, an index (melanin index) is obtained, and the index is applied to the previously determined relationship, thereby making it possible to evaluate and estimate the subject's melanin amount.

Second Embodiment
The skin evaluation method according to the second embodiment is a skin evaluation method that acquires information on light emitted from within skin irradiated with light, and evaluates the skin condition at the basal layer (basement membrane) by utilizing information on green light from the light emitted from within.

Since green light (wavelength 500-600 nm) emitted from inside the skin is mainly reflected by the basal layer (Figure 1) in the skin tissue and emitted from the skin surface, the state of the basal layer can be reflected in image data of the green light emitted from inside the skin. Therefore, according to this embodiment, for example, reflection from the basal layer, elasticity, etc. can be easily evaluated. By evaluating the basal layer according to this embodiment, the possibility of future deterioration of the skin, the healthiness of the skin, etc. can be evaluated.

In this embodiment, in the above-mentioned spectral image data generating step (S3) described with reference to Figure 2, green light spectral image data is generated, and in the index calculation step (S4), an index is calculated using the green light spectral image data. Therefore, the skin evaluation method according to this embodiment, when explained according to the flow shown in Figure 2, may be a skin evaluation method including a step (S1) of irradiating light to the subject's skin, a step (S2) of separating image data of light emitted from inside the skin from image data of all returned light, a step (S3) of generating green light spectral image data from image data of light emitted from inside the skin, a step (S4) of calculating an index using the green light spectral image data, and a step (S5) of evaluating the state of the basal layer (basement membrane) based on the index.

Third Embodiment
The skin evaluation method according to the third embodiment may be a skin evaluation method that acquires information on light emitted from within skin irradiated with light, and evaluates the skin condition in the dermis by utilizing information on red light from the light emitted from within.

Red light (wavelength 600-720 nm) emitted from within the skin is mainly reflected by the dermis in the skin tissue, particularly the papillary layer and/or subpapillary layer (Figure 1), before exiting from the skin surface, so the state of the dermis, particularly the papillary layer and/or subpapillary layer, can be reflected in the image data of the red light emitted from within. Therefore, according to this embodiment, for example, collagen density, blood vessel density, number of capillaries, hemoglobin amount, etc. can be easily evaluated. By evaluating the dermis in this embodiment, it is possible to evaluate skin color (evaluation of skin color considered to be youthful), overall skin elasticity, inflammation, blood circulation state, etc.

In this embodiment, in the above-mentioned spectral image data generating step (S3) described with reference to FIG. 2, red light spectral image data is generated, and in the index calculating step (S4), an index is calculated using the red light spectral image data. Therefore, the skin evaluation method according to this embodiment, when explained according to the flow shown in FIG. 2, may be a skin evaluation method including a step (S1) of irradiating light to the skin of a subject, a step (S2) of separating image data of light emitted from inside the skin from image data of all returned light, a step (S3) of generating red light spectral image data from image data of light emitted from inside the skin, a step (S4) of calculating an index using the red light spectral image data, and a step (S5) of evaluating the condition of the dermis, particularly the papillary layer and/or subpapillary layer, based on the index.

In addition, in the spectral image data generating step (S3), in addition to the spectral image data of red light out of the light emitted from inside the skin, spectral image data of green light out of the light emitted from inside the skin may be generated. Also, in the index calculating step (S4), in addition to the spectral image data of red light out of the light emitted from inside the skin, the index can be calculated using the spectral image data of green light out of the light emitted from inside the skin. In that case, the index can be calculated using the differential image data between the spectral image data of red light out of the light emitted from inside the skin and the spectral image data of green light out of the light emitted from inside the skin. This makes it possible to subtract the influence of the information of green light that reaches the basal layer from the information of the light emitted from inside the skin, so that the state of the dermis can be evaluated with higher accuracy.

=Application Example (Example) of the Third Embodiment=
As an application example of the third embodiment, evaluation of the amount of hemoglobin was studied. Similar to the imaging in the application example of the first embodiment, a skin image of a subject was captured. From the obtained image data (image data of all return light), image data of light emitted from inside the skin was separated, and further, from the image data of light emitted from inside the skin, spectral image data of red light (wavelength 600 to 720 nm) and spectral image data of green light (wavelength 500 to 600 nm) were generated, and differential image data of both spectral image data was obtained. The light intensity in this differential image data was converted to absorbance, and multiplied by a coefficient obtained by multiple regression analysis, and this was used as hemoglobin (index). Meanwhile, the distribution of the amount of hemoglobin in the entire face of each subject was measured from a spectral spectrum obtained using a spectrophotometer, and the average value was used as the "amount of hemoglobin" of the subject. FIG. 9 shows the relationship between the hemoglobin index and the amount of hemoglobin. As shown in FIG. 9, it was confirmed that there is a high correlation between the two.

Therefore, if the relationship shown in Figure 9 is determined in advance, skin image data is obtained from a subject whose skin melanin level is to be evaluated, and image data of red light emitted from within the skin is generated, an index (hemoglobin index) is obtained, and the index is applied to the previously determined relationship, thereby enabling the hemoglobin level of the subject to be evaluated and estimated.

As a further application example of the third embodiment, the evaluation of collagen volume density was investigated. In the same manner as in the evaluation of hemoglobin amount described above, spectral image data of red light (wavelength 600-720 nm) and spectral image data of green light (wavelength 500-600 nm) were generated, and differential image data of both spectral image data was obtained. The light intensity in the spectral image was converted to absorbance, and multiplied by a coefficient obtained by multiple regression analysis to obtain a collagen volume density index (index). Meanwhile, the distribution of collagen volume density index over the entire face of each subject was measured using an acoustic microscope, and the average value of the area was used as the "collagen volume density" of the subject. Figure 10 shows the relationship between collagen volume density index and collagen volume density. As shown in Figure 10, it was confirmed that there is a high correlation between the two.

Therefore, if the relationship shown in Figure 10 is determined in advance, skin image data is obtained from a subject whose skin collagen volume density is to be evaluated, and image data of red light emitted from inside the skin is generated, and in some cases, image data of red light and image data of green light are generated to determine an index (collagen volume density index), which can then be applied to the previously determined relationship to evaluate and estimate the collagen volume density of the subject.

Fourth Embodiment
The skin evaluation method according to the fourth embodiment is similar to the skin evaluation method according to the first embodiment in that it acquires information on emitted light from the inside of the skin irradiated with light and uses information on blue light from the emitted light from the inside, but may also acquire information on total returned light from the skin irradiated with light and evaluate the skin condition in the stratum corneum of the epidermis using the information on blue light from the total returned light and the information on blue light from the emitted light from the inside. In this embodiment, the difference between the information on blue light from the total returned light and the information on blue light from the emitted light from the inside is used.

As described above, blue light (wavelength 380-500 nm) emitted from inside the skin is mainly reflected by the granular layer and/or the spinous layer (Figure 1) in the skin tissue and emitted from the skin surface, so the blue light of this emitted light from inside the skin can reflect the state of the granular layer and/or the spinous layer. On the other hand, the image data of blue light of the total returned light obtained by irradiating light to the subject's skin reflects the state from the granular layer and/or the spinous layer to the stratum corneum, which is an upper layer. Therefore, when blue light spectral image data is generated from the image data of the total returned light, and differential image data is generated by subtracting the image data of blue light of the reflected light from the inside from the image data of the blue light of the total returned light, the differential image data reflects the state of the stratum corneum. Therefore, according to this embodiment, for example, the thickness, transparency, etc. of the stratum corneum can be easily evaluated. For example, by being able to evaluate the transparency of the stratum corneum, dullness, cloudiness, metabolism, etc. of the skin can be evaluated.

In this embodiment, in the above-mentioned spectral image data generating step (S3) described with reference to FIG. 2, spectral image data of blue light is generated from the image data of the total returned light and the image data of the light emitted from inside the skin, and in the index calculating step (S4), an index is calculated using the spectral image data of blue light from the total returned light and the image data of blue light from the light emitted from inside the skin. Therefore, the skin evaluation method according to this embodiment, when explained according to the flow shown in FIG. 2, may be a skin evaluation method including a step of irradiating light to the subject's skin (S1), a step of separating image data of the light emitted from inside the skin from the image data of the total returned light (S2), a step of generating spectral image data of blue light from the image data of the light emitted from inside the skin and a step of generating spectral image data of blue light from the image data of the total returned light (S3), a step of calculating an index using differential image data between the spectral image data of blue light from the light emitted from inside the skin and the spectral image data of blue light from the image data of the total returned light, and a step of evaluating the state of the stratum corneum based on the index (S5).

=Application Example (Example) of the Fourth Embodiment=
As an application example of the fourth embodiment, the turbidity of the stratum corneum was evaluated. Specifically, facial skin images of 134 subjects aged 20 to 79 (22 to 23 subjects for each age group) were taken with an RGB camera. From the obtained image data (image data of all returned light), image data of light emitted from inside the skin was separated, and further, spectral image data of blue light (wavelength 380 to 500 nm) was generated from the image data of light emitted from inside the skin, and spectral image data of blue light was also generated from the image data of all returned light. Furthermore, differential image data between the spectral image data of blue light in the total returned light and the spectral image data of blue light in the light emitted from inside the skin was obtained, and the area average value of the light intensity in the differential image data was taken as the stratum corneum index or turbidity level index (index). Figure 11 shows a graph showing the stratum corneum index versus the age of the subjects. As shown in Figure 11, it was confirmed that the index (turbidity level) of each layer tends to become worse as the age increases. By determining in advance the relationship as shown in FIG. 11, it is possible to estimate an approximate age (skin age or stratum corneum age) based on the stratum corneum index (index) determined based on image data.

The above embodiments can be implemented alone or in combination of two or more. For example, by combining the first embodiment, which uses blue light information to evaluate the amount of melanin, with the third embodiment, which uses red and green light information to evaluate the amount of hemoglobin, it is possible to perform an evaluation of inflammation and melanin production caused by ultraviolet rays. Furthermore, by combining the first to fourth embodiments, it is possible to perform a comprehensive evaluation of the skin, such as determining and evaluating skin age and skin type.

FIG. 12 shows the results of an example of a comprehensive skin evaluation. In the example shown in FIG. 12, the melanin level of the subject's skin was evaluated using the first embodiment described above, the hemoglobin level and collagen level were evaluated using the third embodiment, and the stratum corneum level was evaluated using the fourth embodiment. Furthermore, the results can be compared with the average of each evaluation of people of the same age as the subject, which was obtained in advance. Such a comprehensive skin evaluation can be performed by the relatively simple process of capturing an image of the skin.

In this way, according to this embodiment, since it is possible to evaluate the condition at a specified depth within the skin tissue, it is also possible to evaluate the potential beauty condition of the skin that is not visible to the naked eye. Therefore, the evaluation obtained can be helpful in determining a beauty policy for fundamentally caring for the skin. For example, based on the evaluation obtained by the above-mentioned skin evaluation method, it is possible to appropriately suggest beauty methods, makeup methods, improvements to lifestyle habits, cosmetics, care products, beauty foods, etc.

The present invention has been described above based on specific embodiments, but the above embodiments are presented merely as examples, and the present invention is not limited to the above embodiments. Various changes, modifications, substitutions, deletions, additions, combinations, etc. are possible within the scope of the disclosure of the present invention.

This application claims priority to Japanese Patent Application No. 2022-158733, filed on September 30, 2022, the entire contents of which are incorporated herein by reference.

REFERENCE SIGNS LIST 1 Skin evaluation system 10 Skin evaluation device 20 Imaging device 30 Light source 101 Image acquisition unit 102 Calculation unit 103 Evaluation unit 1001 CPU
1002 ROM
1003 RAM
1004 Auxiliary storage device 1005 Display device 1006 Operation device 1007 I/F device 1008 Drive device 1009 Storage medium

Claims

Obtaining information on the light emitted from inside the irradiated skin,
The skin evaluation method uses information on light of a predetermined wavelength among the light emitted from the inside to evaluate the condition of the skin at a predetermined depth.
The skin evaluation method according to claim 1, wherein the light emitted from the inside includes visible light.
The skin evaluation method according to claim 1 or 2, wherein the information on the light of the specified wavelength includes a statistic of the light intensity in the evaluation target area or the absorbance calculated from the light intensity.
The skin evaluation method according to claim 2, further comprising: evaluating a state of the epidermis by utilizing information of blue light and/or green light among the light emitted from the inside; and/or evaluating a state of the dermis by utilizing information of red light among the light emitted from the inside.
assessing the condition of the epidermis,
Using information on blue light from the light emitted from the inside, a state of the granular layer and/or the spinous layer is evaluated;
The skin evaluation method according to claim 4 , further comprising evaluating one or more of a melanin amount and an epidermal thickness based on the state of the granular layer and/or the spinous layer.
assessing the condition of the epidermis,
evaluating the state of the basal layer using information on green light from the light emitted from the inside;
The skin evaluation method according to claim 4 , further comprising evaluating one or more selected from the group consisting of reflected light from a basement membrane and elasticity of the basement membrane based on the state of the basal layer.
assessing the condition of the dermis
evaluating a state of the dermis using information on red light from the light emitted from the inside;
The skin evaluation method according to claim 4 , further comprising evaluating one or more selected from a collagen state, a blood vessel state, and a hemoglobin amount based on the state of the dermis.
assessing the condition of the epidermis,
Furthermore, information on the total return light from the skin irradiated with the light is obtained;
The skin evaluation method according to claim 4 , further comprising evaluating a state of the stratum corneum by utilizing a difference between information on the total returned light and information on green light among the light emitted from the inside.
The skin evaluation method according to claim 8, wherein one or more selected from stratum corneum transparency and stratum corneum thickness are evaluated based on the state of the stratum corneum.
assessing the condition of the dermis
The skin evaluation method according to claim 7 , further comprising evaluating a state of the dermis by utilizing a difference between information on red light among the light emitted from the interior and information on green light among the light emitted from the interior.
The skin evaluation method according to claim 1 or 2, which determines one or more selected from skin age and skin type based on the evaluation of the skin condition at a predetermined depth.
Obtaining information about the light emitted from the inside
3. The skin evaluation method according to claim 1, further comprising projecting a pattern onto a skin region to be evaluated, the pattern forming an irradiated region where light is irradiated and a non-irradiated region where light is not irradiated, and acquiring information on light from the non-irradiated region.
evaluating the condition of the skin at a predetermined depth includes calculating an index including one or more selected from an average value, a maximum value, a minimum value, a median value, an integral value, a sum value, a standard deviation, a variance, a skewness, and a kurtosis of the light intensity in the evaluation target area or the absorbance calculated from the light intensity;
The skin evaluation method according to claim 3 , further comprising evaluating a condition of the skin at a predetermined depth based on the index.
A skin evaluation device comprising: an information acquisition unit that acquires information on light emitted from inside skin irradiated with light; and an evaluation unit that evaluates a condition of the skin at a predetermined depth using information on light of a predetermined wavelength among the light emitted from the inside.
A program for causing a computer to function as an information acquisition unit that acquires information on light emitted from inside the skin irradiated with light, and an evaluation unit that evaluates the condition of the skin at a predetermined depth using information on light of a predetermined wavelength among the light emitted from the inside.