Skin evaluation method and powder evaluation method

Abstract

To provide a method for evaluating freshness and firmness of skin.SOLUTION: A skin evaluation method includes a feature extraction step for extracting an optically detectable feature from a subject's skin image, and an evaluation step for evaluating freshness and firmness of the subject's skin on the basis of the coefficient of variation, where the feature is a coefficient of variation of brightness in a measurement area set in the skin image.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for evaluating skin and a method for evaluating powder. [Background technology]

[0002] People give a wide variety of impressions to others depending on various factors such as their appearance, speech, and behavior. Among these, visual information, especially the appearance of a face, is one of the most important factors that determine a person's impression.

[0003] For this reason, research is being conducted into techniques for acquiring parameters that affect the appearance of a person's face. For example, Patent Document 1 discloses a technique for measuring the luminance of a measurement target part on a subject's face, generating a histogram, and evaluating the subject's skin condition from the shape of the histogram.

[0004] Patent Document 2 discloses a technique for estimating the age of a subject by acquiring a facial image of the subject and calculating the intensity of spatial frequencies therefrom.

[0005] Additionally, skin firmness has been attracting attention as a factor in creating a youthful impression, and methods for visually evaluating skin firmness have been developed. Patent Document 3 discloses a method for evaluating a subject's sense of cosmetic firmness by calculating the area ratio of high-luminance regions to medium-luminance regions, or the perimeter ratio of medium-luminance regions, from a luminance gradation image. Patent Document 4 discloses a method for evaluating the firmness of a subject's facial skin by calculating the amount of glossy areas and wrinkled areas present on the skin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-131336 A [Patent Document 2] Re-table No. 2011-162050 [Patent Document 3] JP 2008-93048 A [Patent Document 4] JP 2017-12337 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors have conducted extensive research into whether the freshness and firmness of skin can be evaluated using luminance values ​​extracted from photographed images of the skin. As a result, they have discovered that the coefficient of variation of luminance in photographed images of the skin is related to the freshness and firmness of the skin.

[0008] In view of the above circumstances, an object of the present invention is to provide a method for evaluating the moisture and firmness of skin. Another object of the present invention is to provide a powder evaluation method for selecting powder that imparts moisture and firmness to the skin. [Means for solving the problem]

[0009] The present invention, which solves the above-mentioned problems, comprises: a feature extraction step of extracting optically detectable feature amounts from a skin image of a subject; and an evaluation step of evaluating the freshness and firmness of the subject's skin based on the feature amount, In this skin evaluation method, the feature amount is a coefficient of variation of brightness within a measurement area set in the skin image.

[0010] In this way, by using the brightness variation coefficient as an optically detectable feature amount, it is possible to evaluate the moisture and firmness of the skin.

[0011] In a preferred embodiment of the present invention, a high luminance area in the skin image is further acquired as the feature amount. By using the two feature quantities, the coefficient of variation of brightness and the high brightness area, it is possible to more accurately evaluate the moisture and firmness of the skin.

[0012] In a preferred embodiment of the present invention, in the evaluation step, the subject's skin is evaluated as having moisture and firmness when the value of the coefficient of variation is 0.065 or less and the high luminance area is 12,000 pixels or more.

[0013] The present invention provides a powder evaluation method, comprising the steps of: The evaluation powder is applied to a skin substitute having a convex curved surface; an image acquisition step of acquiring an image of the surface of the substitute to which the evaluation powder has been applied; a feature extraction step of extracting optically detectable feature amounts from the image; and an evaluation step of evaluating the cosmetic effect of the evaluation powder based on the feature amount, The feature amount also relates to a powder evaluation method, in which the feature amount is a coefficient of variation of brightness in the image.

[0014] By calculating the coefficient of variation of brightness, it is possible to select powders that impart a cosmetic effect of giving freshness and firmness to the skin.

[0015] The present invention also provides a feature extraction means for extracting optically detectable feature amounts from a skin image of a subject; and an evaluation means for evaluating the freshness and firmness of the skin of the subject based on the feature amount, The feature amount is a coefficient of variation of brightness within a measurement area set on the skin image, in the skin evaluation device.

[0016] The present invention also provides a computer comprising: A feature extraction means for extracting optically detectable features from a skin image of a subject; a skin evaluation program for causing the program to function as an evaluation means for evaluating freshness and firmness of the skin of the subject based on the feature amount, The feature amount is a coefficient of variation of brightness within a measurement area set on the skin image. Effect of the Invention

[0017] According to the skin evaluation method of the present invention, it is possible to evaluate the skin that provides moisture and firmness. Furthermore, according to the powder evaluation method of the present invention, it is possible to select powders that have the cosmetic effect of imparting moisture and firmness to the skin. [Brief description of the drawings]

[0018] [Figure 1] 13 is a diagram for explaining the setting position of the evaluation region of the subject's skin when the luminance variation coefficient is extracted as a feature amount. FIG. [Diagram 2] 1 is a hardware block diagram showing an embodiment of a skin evaluation device of the present invention. [Diagram 3] 1 is a graph showing the relationship between the moisture and firmness of the skin and the coefficient of variation of luminance in Example 1. [Figure 4] 1 is a graph showing the relationship between the moisture and firmness of the skin and the coefficient of variation of brightness in Example 1, where (a) shows the evaluation results of a panelist with moisture and firm skin, and (b) shows the evaluation results of a panelist with lacking moisture and firmness in the skin. [Diagram 5] 13 is a table showing the results of extracting the luminance variation coefficient and high luminance area as feature amounts for bare skin and skin after application of a cosmetic material in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the embodiments of the present invention will be described for the purpose of understanding the present invention. Note that the following embodiments are examples of the present invention, and can be modified as appropriate within the scope of the claims.

[0020] [1] Skin evaluation method The skin evaluation method of the present invention includes an image acquisition step of acquiring a skin image of a subject, a feature extraction step of extracting optically detectable features from the skin image, and an evaluation step of evaluating the moisture and firmness of the subject's skin based on the features.

[0021] Examples of the "optically detectable feature" in the present invention include the area of ​​a high-luminance region having a luminance higher than a predetermined luminance (high-luminance area), a pattern of luminance contour lines, the complexity of a medium-luminance region, or a coefficient of variation of luminance. In the present invention, the coefficient of variation of luminance is extracted as the feature amount.

[0022] Next, the skin evaluation method of the present invention will be described in detail by taking examples of each feature amount to be extracted.

[0023] (1) Luminance variation coefficient A method for evaluating skin when the coefficient of variation of luminance is used as the feature amount will be described in detail below.

[0024] (i) Image acquisition process In the image acquisition step, a skin image of the subject is acquired. As the skin image, a skin image of the cheek region is preferably used. Here, the skin image may be an image captured by a general video camera or digital camera.

[0025] It is preferable that the skin image has a resolution that can withstand image analysis in a later step. When capturing an image, the resolution of the image may be appropriately set according to the number of pixels from which a feature amount described below can be extracted.

[0026] Furthermore, the skin evaluation method of the present invention does not necessarily include a step of capturing a skin image, and the following steps may be carried out using a previously acquired skin image.

[0027] (ii) Feature extraction process Next, image processing is performed on the acquired skin image. In the present invention, it is preferable to convert to 8-bit grayscale (256 gradations). In addition, in the image processing, the number of pixels of the image is preferably 2000×2000 to 1200×1200 pixels, and more preferably 1800×1800 to 1400×1400 pixels. Specifically, it is preferable to make the acquired skin image an image with a number of pixels of 1600×1600 pixels.

[0028] In addition, in image processing, in order to remove noise in the image, it is possible to process the image with an averaging filter. In the present invention, it is preferable to use an image that has been subjected to averaging filter processing 1 to 3 times.

[0029] Next, an evaluation region for extracting feature quantities is set on the skin image, which is preferably set to a medium to high luminance region of the cheek.

[0030] Here, the "high luminance region" in the present invention refers to a region in an image having a luminance higher than a predetermined luminance. For example, the luminance can be directly extracted in image processing, and the luminance within a certain range from the highest luminance (maximum luminance) in the image can be determined as the high luminance region. Specifically, for an image that has been subjected to gradation conversion, a portion having a certain gradation or more can be determined as the high luminance region. More specifically, based on the maximum luminance, the region can be preferably the top 75% or more, more preferably the top 78% or more, and even more preferably the top 80% or more.

[0031] Also, a specific luminance range may be defined as a high luminance region. For example, when an image is converted to 8-bit grayscale (256 gradations) in image processing, it is preferable to define a region of 200 gradations or more as a high luminance region.

[0032] In addition, the mid-luminance region in the present invention can be defined as a specific range of gradation, and more specifically, the mid-luminance region can be defined as the uppermost 55 to 75%, more preferably the uppermost 60 to 73%, and even more preferably the uppermost 62 to 71%, with the highest luminance being the highest point.

[0033] Also, a specific luminance range may be defined as the mid-luminance region. For example, when an image is converted to 8-bit grayscale (256 gradations) in image processing, it is preferable to define a range of 160 to 180 gradations as the mid-luminance region.

[0034] In the present invention, when the luminance is specified by a specific numerical value, the luminance indicates a pixel value when an image is converted into an 8-bit grayscale (256 gradations).

[0035] The evaluation region is preferably set in a range of luminance from 150 to 185 gradations, more preferably from 155 to 185 gradations, and even more preferably from 160 to 180 gradations. Specifically, the evaluation area can be determined by the following method. That is, the intersection of a perpendicular line drawn from the side of the eye and a horizontal line drawn from the side of the nostril is used as the reference point, and a certain range from the intersection can be determined as the evaluation area. For example, when an image of the left cheek is used, a rectangular range of 300 x 240 pixels to the lower left of the intersection can be determined as evaluation area A (see FIG. 1).

[0036] Next, the luminance within the evaluation area is extracted for each pixel, and the coefficient of variation is calculated using the standard deviation and average value obtained from the extracted luminance.

[0037] (iii) Feature evaluation process In the evaluation step, when the calculated coefficient of variation of luminance is equal to or less than a predetermined value, the subject's skin can be evaluated as having moisture and firmness. Specifically, when the value of the brightness variation coefficient calculated in the feature extraction process is preferably 0.065 or less, more preferably 0.063 or less, and even more preferably 0.060 or less, the subject's skin can be evaluated as having freshness and firmness.

[0038] (2) High-luminance area A method for evaluating skin when a high luminance area is used as a feature amount will be described in detail below.

[0039] (i) Image acquisition process The procedure of the image acquisition step can be based on the description of (1) Brightness variation coefficient above.

[0040] (ii) Feature extraction process Next, the acquired skin image is subjected to image processing. The image processing is preferably performed by converting the image into an 8-bit grayscale (256 gradations). For details of the image processing, the description of the above (1) Luminance variation coefficient can be used.

[0041] In the image processing step, a contour line may be provided for every 10 to 20 gradations on the image converted to 8-bit grayscale (256 gradations) to create a contour line image. By using the resulting contour line image, the range for extracting high-luminance areas can be clarified.

[0042] Next, a high luminance area is extracted from the obtained skin image. The high luminance area is preferably extracted by calculating the number of pixels in the high luminance area of ​​the image. The range of the "high-luminance region" in extracting the high-luminance area can be set in the same manner as the (1) coefficient of variation of luminance. Specifically, when the image is converted to 8-bit grayscale (256 gradations) in image processing, it is preferable to define the region of 200 gradations or more as the high-luminance region.

[0043] (iii) Feature evaluation process In the evaluation step, when the calculated high luminance area is equal to or greater than a predetermined value, the subject's skin can be evaluated as having moisture and firmness. Specifically, when the high-brightness area extracted in the feature extraction process is preferably 12,000 pixels or more, more preferably 13,000 pixels or more, and more preferably 14,000 pixels or more, the subject's skin can be evaluated as having moisture and firmness.

[0044] The skin evaluation method of the present invention preferably extracts a luminance variation coefficient and a high luminance area as feature quantities, and evaluates the moisture and firmness of the skin based on both values. By using both the luminance variation coefficient and the high luminance area as indices, the moisture and firmness of the skin can be evaluated more accurately.

[0045] The present invention may also be a method for evaluating skin using two or more different skin images. That is, feature amounts are extracted from each of the multiple skin images, and the moisture and firmness of the skin can be evaluated based on the obtained feature amounts.

[0046] The multiple skin images may be acquired from different skin regions of the same subject, or may be acquired from the same skin region of the same subject.

[0047] When skin images obtained from the same skin area are used, a skin image (first skin image) is obtained from a specific skin area at a certain point in time (first point in time), and then a skin image (second skin image) is obtained again from the same skin area later (i.e., at a second point in time), and the skin's moisture and firmness can be evaluated based on the features calculated from each skin image.

[0048] An example of the above embodiment is a form in which the moisture and firmness of the skin before the use of the cosmetic product is compared with the moisture and firmness of the skin after the use of the cosmetic product. That is, a skin image (first skin image) of the skin (e.g., bare skin) of a subject before the use of the cosmetic product is obtained, a skin image (second skin image) of the same subject after the use of the cosmetic product is obtained, and the feature amounts obtained from the first skin image and the second skin image are compared to evaluate the moisture and firmness of the subject's skin.

[0049] The above-mentioned cosmetic may be any basic cosmetic used for skin care, such as a lotion, milky lotion, or serum, or a makeup cosmetic, such as a foundation or base, but the present invention is preferably used to evaluate the freshness and firmness of the skin before and after the use of a makeup cosmetic.

[0050] In this way, when evaluating the skin moisture and firmness of the same skin area at different points in time, (iii) the feature evaluation process can be performed by determining whether or not the feature satisfies a reference value, as described above, or by comparing features derived from multiple skin images with each other, as described below.

[0051] For example, when the coefficient of variation of brightness is used as a feature, if the coefficient of variation at the second time point is smaller than the coefficient of variation at the first time point, the subject's skin can be evaluated as having moisture and firmness.

[0052] When the high-luminance area is used as the feature amount, if the high-luminance area at the second time point is larger than the high-luminance area at the first time point, the subject's skin can be evaluated as having moisture and firmness.

[0053] In addition, for the analysis of the high brightness area and the brightness variation coefficient described above, known image processing software such as the open source "ImageJ" can be used.

[0054] Furthermore, the skin evaluation method of the present invention can be used for evaluating a customer's skin for beauty purposes such as sales of cosmetics, counseling, and esthetics.

[0055] [2] Powder evaluation method The powder evaluation method of the present invention includes an image acquisition step of acquiring an image of the surface of a skin substitute to which an evaluation powder has been applied, a feature extraction step of extracting optically detectable features from the image, and an evaluation step of evaluating the cosmetic effect of the evaluation powder based on the features.

[0056] The feature amount can be determined by referring to the description in the above-mentioned [1] Skin evaluation method, and it is particularly preferable to extract the luminance variation coefficient as the feature amount.

[0057] Next, a detailed description will be given of the powder evaluation method of the present invention when the coefficient of variation of brightness is used as the characteristic amount.

[0058] (i) Image acquisition process First, the evaluation powder is applied to the surface of the skin substitute. It is preferable to apply a certain amount of emulsion and then apply a specified amount (e.g., 0.1 g) of the evaluation powder evenly with a brush or fingers.

[0059] Here, the skin substitute used in the powder evaluation method of the present invention is preferably one that imitates human skin in terms of color, texture, elasticity, surface shape such as pores, etc. For example, commercially available artificial skin, three-dimensional skin models, dolls, balloons, fruits, synthetic leather, etc. can be used as skin substitutes and the evaluation powder can be applied thereto to analyze the feature quantities. In the present invention, a three-dimensional skin model or doll with a central convexity is preferably used. An example of such a three-dimensional skin model is the Bioskin Elasticity Model manufactured by Bealux.

[0060] Alternatively, a sample that mimics the changes in the surface shape of the skin, such as pores, when a person's facial expression changes may be prepared and used as a substitute for the skin. By using such a sample, it is possible to easily evaluate whether the application of the powder produces the desired cosmetic effect.

[0061] Next, an image of the three-dimensional skin model is obtained while irradiating a certain amount of light from the vertical direction above the skin substitute after application. The irradiation angle of the light irradiated onto the three-dimensional skin model is set so that the light is evenly irradiated onto the three-dimensional skin model by setting the light source on an extension line extending vertically from the apex of the three-dimensional model. In addition, it is preferable to adjust the amount of light irradiated onto the three-dimensional skin model so that the high brightness area of ​​the skin substitute before application of the evaluation powder is 3% to 35% or less of the total area of ​​the skin substitute.

[0062] (ii) Feature extraction process Luminance is extracted from the image obtained in the above-mentioned image acquisition step, and the standard deviation and average value obtained from the luminance are used to calculate the coefficient of variation. The coefficient of variation is preferably calculated using the luminance value in the medium luminance or lower range, and is preferably calculated using a value of 180 gradations or lower, more preferably 170 gradations or lower, and particularly preferably 160 gradations or lower.

[0063] In the extraction process, a portion of the skin substitute in the acquired image that can be recognized as a skin substitute is set as the extraction target area. For example, when a three-dimensional skin model with a convex center is used, a dome portion that can be used as a skin substitute is set as the extraction target area.

[0064] When calculating the luminance variation coefficient using a centrally convex three-dimensional skin model, it is preferable to extract the luminance distributed on a perpendicular line drawn at the center of the three-dimensional skin model in the image. Specifically, a vertical line is drawn at the center of the three-dimensional skin model image, and the luminance on the perpendicular line is extracted. Among the obtained luminance, the variation coefficient calculated using the luminance value of 160 gradations or less can be used as the luminance variation coefficient value used in the evaluation process described below.

[0065] (iii) Feature evaluation process In the evaluation step, the calculated coefficient of variation of brightness is evaluated. In the present invention, when the coefficient of variation of brightness is preferably 0.08 or less, more preferably 0.07 or less, and even more preferably 0.06 or less, the powder to be evaluated can be evaluated as a powder that contributes to the cosmetic effect of imparting moisture and firmness to the skin.

[0066] The powder evaluation method of the present invention may be used to evaluate a powder consisting of a single component, or may be used to evaluate a mixture of multiple powders.

[0067] [3] Skin evaluation device The skin evaluation device of the present invention will be described below with reference to Fig. 2. The color unevenness display device of the present invention is a device for implementing the skin evaluation method described in the above item [1]. Therefore, the description of the above item [1] also applies to the following device.

[0068] As shown in Figure 2, the skin evaluation device 1 of the present invention comprises an image acquisition means 11 that acquires a skin image of a subject, a feature extraction means 12 that extracts optically detectable features from the skin image, an evaluation means 13 that evaluates the moisture and firmness of the subject's skin based on the features obtained by the feature extraction means 12, a memory unit 14 that stores various equations required for feature extraction and skin evaluation, and a display means 15 that transmits the skin evaluation results to an arbitrary display device.

[0069] The image acquisition means 11 is for capturing an image of the surface of the skin, inputting the image of the surface of the skin and converting it into a signal that quantifies the color elements. The signal is not particularly limited as long as it can represent the skin condition, but for example, RGB signals, Munsell signals, L * a * b * Examples of such signals include a signal (JIS Z8729), an XYZ signal, a signal representing brightness, hue and saturation, etc. As the image acquisition means 11, a general video camera or digital camera can be used.

[0070] The feature extraction means 12 extracts a predetermined feature from the skin image output from the image acquisition means 11. As the feature, the feature described in [1] can be preferably exemplified, and among them, it is preferable to extract the brightness variation coefficient. In addition to the brightness variation coefficient, a form in which a high brightness area is extracted as the feature can also be preferably exemplified.

[0071] The evaluation means 13 evaluates the freshness and firmness of the subject's skin based on the features obtained by the feature extraction means 12.

[0072] The storage unit 14 stores programs necessary for the functioning of the skin evaluation device of the present invention, as well as various formulas necessary for extracting features and evaluating skin.

[0073] The display means 15 transmits the skin evaluation results obtained by the evaluation means 13 to an arbitrary display device. An example of the arbitrary display device is a liquid crystal display.

[0074] It should be noted that the present invention does not necessarily have to have the above-mentioned configuration, and may take the form of a skin evaluation device that includes, for example, feature extraction means 12 that extracts optically detectable features from a skin image of the subject, and evaluation means 13 that evaluates the moisture and firmness of the subject's skin based on the features obtained by feature extraction means 12.

[0075] [4] Skin evaluation program The skin evaluation program of the present invention causes a computer, other device, machine, etc. to function as image acquisition means 11 for acquiring a skin image of a subject, feature extraction means 12 for extracting optically detectable features from the skin image, evaluation means 13 for evaluating the moisture and firmness of the subject's skin based on the features obtained by the feature extraction means 12, a memory unit 14 for storing various formulas necessary for feature extraction and skin evaluation, and display means 15 for transmitting the skin evaluation results to an arbitrary display device (see Figure 2).

[0076] Here, the feature extraction means 12 is characterized in that it extracts a luminance variation coefficient as the feature.

[0077] In the present invention, it is not necessary for the program to cause all of the above-mentioned components to function. For example, the program may be in the form of a skin evaluation program that causes a computer, other device, machine, etc. to function as feature extraction means 12 that extracts optically detectable features from a skin image of the subject, and evaluation means 13 that evaluates the moisture and firmness of the subject's skin based on the features obtained by feature extraction means 12.

[0078] The skin evaluation program of the present invention is a program related to the above-mentioned [1] skin evaluation method and [3] skin evaluation device. Therefore, the above-mentioned [1] and [3] descriptions are also applicable to the skin evaluation program of the present invention. EXAMPLES

[0079] Example 1 The correlation between the moisture and firmness of the panelists' skin and the coefficient of variation of luminance was evaluated according to the following procedure.

[0080] <Evaluation Procedure> (1) Selection of panelists (1-1) Women in their 20s to 40s (N=48) were selected as panelists, and their bare skin was photographed using VISIA (registered trademark) Evolution.

[0081] (1-2) Based on the obtained skin images, the panelists were classified into three categories: "those with moisture and firmness," "those without moisture and firmness," and "can't say." Of these, nine panelists with significant moisture and firmness and nine panelists without moisture and firmness were selected.

[0082] (2) Image processing (2-1) The obtained skin image was processed with an averaging filter to adjust the pixels, and then converted to 8-bit grayscale (256 gradations).

[0083] (2-2) For the converted skin image, the intersection of a vertical line from the side of the eye and a horizontal line from the side of the nostril was used as the reference point, and a rectangular area of ​​300 x 240 pixels from the center to the lower left was used as the evaluation area. The brightness within the evaluation area was 160 to 180 gradations.

[0084] (2-3) The average value and standard deviation of the brightness in the evaluation area were calculated for each pixel, and the coefficient of variation of the brightness was calculated using these values. Image J was used as the image processing software.

[0085] (2-4) In addition, for the skin image converted to 8-bit grayscale (256 gradations), contour lines were set every 10 to 20 gradations using Excel contour lines, and a separate contour image was created.

[0086] <Result> As shown in Figure 3, a significant difference was observed in the coefficient of variation of brightness between panelists whose skin was classified as "moist and firm" and those whose skin was classified as "not moist and firm." This revealed that people whose skin was moist and firm had a smaller coefficient of variation of skin.

[0087] FIG. 4 shows the correspondence between the photographs showing the actual skin conditions of "people with moisture and firmness" (panelers 1 to 3) and "people without moisture and firmness" (panelers 4 to 6) and the coefficient of variation of brightness. Panelists 1 to 3, whose skin was classified as "fresh and firm," had a coefficient of variation of brightness within the evaluation area lower than 0.05 (Figure 1). 4 On the other hand, panelists 4 to 6, whose skin was classified as "lacking moisture and firmness," had a higher coefficient of variation within the evaluation range than panelists 1 to 3 (Figure 1). 4 (b)).

[0088] From the above, it became clear that there is a correlation between the coefficient of variation of luminance and the moisture and firmness of the skin.

[0089] Example 2 Panelist 7, whose skin was evaluated as fresh and firm, was photographed using VISIA® Evolution to capture the bare skin and the skin condition after applying cream foundation. Skin images were taken of the area including the cheeks. From the obtained skin images, the coefficient of variation of brightness and high brightness area were calculated as features, and the freshness and firmness of the skin before and after the application of foundation were evaluated.

[0090] The luminance variation coefficient was calculated in the same manner as in (2) Image processing in Example 1 above. 5 The contour image in shows the cheek area of ​​panelist 7 after image editing, and the rectangle on the cheek shows the evaluation area for the luminance variation coefficient. The calculation of the high luminance area was performed according to the following procedure.

[0091] -Calculation of high brightness area As in (2-4) above, a contour image was obtained from the skin image. In the obtained contour image, areas with 200 gradations or more were extracted as high brightness areas.

[0092] <Result> As shown in Figure 5, the skin after foundation application had a decreased coefficient of variation in luminance and an increased high luminance area compared to bare skin. Therefore, it can be determined that the application of foundation improved the freshness and firmness of the skin of panelist 7.

[0093] In this way, by using the skin evaluation method of the present invention, changes in skin moisture and firmness before and after application of a cosmetic material such as foundation can be easily and accurately evaluated. [Industrial Applicability]

[0094] The present invention can be used for evaluating a customer's skin in situations such as cosmetic sales, counseling, and esthetics, as well as for evaluation and design in the research and development of cosmetics. [Explanation of symbols]

[0095] 1. Skin evaluation device 11 Image acquisition method 12 Feature extraction method 13. Evaluation methods 14 Storage section 15 Display means

Claims

1. A feature extraction step of extracting optically detectable features from a skin image of a subject; and an evaluation step of evaluating the freshness and firmness of the subject's skin based on the feature amount, the feature amount is a coefficient of variation of luminance within a measurement area set on the skin image, A skin evaluation method, wherein in the evaluation step, the subject's skin is evaluated as having moisture and firmness if the value of the coefficient of variation is 0.065 or less.

2. The method further comprises acquiring a high luminance area in the skin image as the feature amount, The skin evaluation method according to claim 1 , wherein the high luminance area is an area of ​​a region that is in the top 75% or more of a maximum luminance, which is the highest luminance in the image.

3. 3. The skin evaluation method according to claim 2, wherein in the evaluation step, the subject's skin is evaluated as having moisture and firmness if the value of the coefficient of variation is 0.065 or less and the high-luminance area is 12,000 pixels or more.

4. A feature extraction means for extracting optically detectable features from a skin image of a subject; and an evaluation means for evaluating the freshness and firmness of the subject's skin based on the feature amount, the feature amount is a coefficient of variation of luminance within a measurement area set on the skin image, The skin evaluation device, wherein the evaluation means evaluates the subject's skin as having moisture and firmness when the value of the coefficient of variation is 0.065 or less.

5. Computer, A feature extraction means for extracting optically detectable features from a skin image of a subject; a skin evaluation program for causing the program to function as an evaluation means for evaluating freshness and firmness of the skin of the subject based on the feature amount, the feature amount is a coefficient of variation of luminance within a measurement area set on the skin image, A skin evaluation program, wherein the evaluation means evaluates the subject's skin as having moisture and firmness when the value of the coefficient of variation is 0.065 or less.

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