JP2013520274A - Skin hue measuring system and method - Google Patents

Abstract

  The skin hue measurement system includes a conversion module that converts a hue of an image obtained by photographing skin into hue data on a log coordinate system having a coordinate axis corresponding to a primary color; a preset illumination vector and a plurality of pigment vectors; A first measurement module arranged in a polygonal pyramid shape surrounding the hue data, and measuring yellowness using the vertex positions of the polygonal pyramid; and the hue data, the component of the illumination vector direction and the direction of each pigment vector A second measurement module for measuring a plurality of pigment distributions separately. By using the skin hue measurement system, it is possible to measure the yellowness, blackness and / or redness of the skin, and the measurement results can be output as an image, and the skin tone before and after using a specific cosmetic product It is possible to display the change of the information easily and visually.

Description

  Embodiments relate to a skin hue measurement system and method.

The technique of measuring the texture or hue of the skin and reproducing it with an image on a computer has been considered as an important function in various imaging systems. Particularly recently, with the development of mobile devices equipped with charge coupled devices (CCDs), cosmetic diagnosis systems, and telemedicine, the technology for accurately measuring the texture or hue of skin has been developed for image communication and skin. The degree of utilization for selection of appropriate cosmetics or medical diagnosis is increasing.
As a conventional method used for measuring the texture or hue of the skin, there is a method of extracting a distribution of melanin and hemoglobin present in the skin from an image obtained by photographing the skin with a digital camera. For example, a method for extracting the distribution of melanin and hemoglobin from an image is described in “Independent component analysis of skin color image” published in 1999 in the Journal of the Optical Society of America. There are methods described in a paper by Tsumura et al.
However, when using such a conventional method, it is impossible to measure the basic color of the skin, which differs from person to person, separately from the amount of the pigment. There is a problem that it is difficult to accurately reflect the effect of.

  According to one aspect of the present invention, yellowness representing a basic skin tone and blackness and redness due to skin pigments can be measured from an image obtained by photographing the skin. It is possible to provide a skin hue measurement system and method that can easily observe a change in redness as an image.

A skin hue measurement system according to an embodiment includes a conversion module that converts a hue of an image obtained by photographing skin into hue data on a log coordinate system having coordinate axes corresponding to primary colors; A first measurement module that arranges a pigment vector in a polygonal pyramid shape surrounding the hue data and measures yellow using a position of a vertex of the polygonal pyramid; and the hue data as a component in the illumination vector direction; A second measurement module may be included that measures a plurality of dye distributions separately into components in the respective dye vector directions.
A skin hue measurement method according to an embodiment includes a step of converting a hue of an image obtained by photographing skin into hue data on a log coordinate system having a coordinate axis corresponding to a primary color; a preset illumination vector and a plurality of pigments Arranging a vector in a polygonal pyramid shape surrounding the hue data; measuring yellow using a position of a vertex of the polygonal pyramid; and the hue data as a component in the illumination vector direction and the respective The method may include a step of measuring a plurality of dye distributions by separating them into components in the dye vector direction.

  If the system and method for measuring skin hue according to one aspect of the present invention are used, the hue data generated by projecting the hue of each pixel on an RGB log (log) coordinate system from an image obtained by photographing the skin, the illumination vector, It is possible to measure the yellowness, blackness and / or redness of the skin by separating the components in the direction of each pigment vector. Moreover, the measurement result can be output as an image, and the change in skin tone before and after the use of a specific cosmetic product can be easily and visually displayed.

FIG. 1 is a block diagram of a skin hue measurement system according to an embodiment. FIG. 2 is a graph showing hue data obtained by projecting an image of skin onto an RGB log coordinate system. FIG. 3a is a graph showing hue data obtained using images obtained by photographing different subjects' skins. FIG. 3 b is a graph showing hue data obtained using images obtained by photographing the skins of different subjects. FIG. 3c is a graph showing hue data obtained using images obtained by photographing different subjects' skins. FIG. 4A is a schematic diagram illustrating output forms of redness, blackness, and yellowness in the skin hue measurement system according to an embodiment. FIG. 4B is a schematic diagram illustrating output forms of redness, blackness, and yellowness in the skin hue measurement system according to an embodiment. FIG. 4 c is a schematic diagram illustrating output forms of redness, blackness, and yellowness in the skin hue measurement system according to an embodiment. FIG. 5 is a flowchart of a skin hue measuring method according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram of a skin hue measurement system according to an embodiment.
Referring to FIG. 1, the skin hue measurement system may include a conversion module 20, a first measurement module 30, and a second measurement module 40. In other embodiments, the skin hue measurement system may further include the imaging module 10 and / or the output module 50. In this specification, a unit, a module, a system, or the like may refer to hardware, a combination of hardware and software, or software for implementing a specific function. For example, a unit, a module, or a system may refer to a process, a processor, an object, an executable file, an execution thread, a thread of execution, or a program. , It may refer to both a specific application and a device for performing it.

  The photographing module 10 is a part for photographing the subject's skin as an image. For example, the imaging module 10 may include a moving device equipped with a charge coupled device (CCD), a digital camera, or the like, and may capture an image of the subject's skin to generate an image. In one embodiment, the imaging module 10 may be configured as part of a skin hue measurement system. However, in another embodiment, the skin hue measurement system may not include the photographing module 10 and may perform only the hue measurement by receiving the skin image of the subject image photographed using a separate device. Good.

The conversion module 20 converts the hue of each pixel of the captured skin image into an RGB log formed by coordinate axes corresponding to the primary colors of red (R), green (G), and blue (B). This is a part for generating hue data by projecting to a coordinate system. It can be understood that the skin hue is expressed by darkening the light indicating the basic color of the skin with a pigment such as melanin or hemoglobin. When the hue expressed from the _skin is c _skin , the basic color of the skin is c _base , the amount of melanin in the skin is m, and the amount of hemoglobin in the skin is h, the hue c _skin expressed from the _skin is expressed by the following formula 1 Can be modeled.

In Equation 1, σ _m and σ _h are absorption coefficients of melanin and hemoglobin, respectively, and k _light is a scalar value indicating the effect of light contributing to the hue expressed from the skin. When there is no skin pigment, the hue expressed from the skin is _cbase · k _light . When there is a pigment such as melanin and / or hemoglobin in the skin, the light expressed from the skin decreases exponentially from the basic color of the skin as the amount of pigment increases.

  On the other hand, if the log of both sides of the above-mentioned formula 1 is taken, it can be converted into a linear form like the following formula 2.

As shown in Equation 2, light expressed from the skin corresponds to -log (c _base ) corresponding to the basic color of the skin, -log (k _light ) corresponding to the lighting effect, and light absorption by melanin. It can be expressed by a linear sum of σ _m m and σ _h h corresponding to light absorption by hemoglobin.

Equations 1 and 2 described above may be applied independently for each of red (R), green (G), and blue (B). That is, each term of Equation 2 may be represented by a three-dimensional vector having components corresponding to the colors red (R), green (G), and blue (B). In the present specification, this is called an RGB vector. In the present specification, -log (c _base ) is referred to as a basic color vector, -log (k _light ) is referred to as an illumination vector, σ _m is referred to as a melanin vector, and σ _h is referred to as a hemoglobin vector. That is, the hue expressed from the skin may be expressed as a vector sum of a basic color vector, an illumination vector, and a plurality of pigment vectors (for example, a melanin vector and a hemoglobin vector).

  In the skin hue measurement system and method according to the embodiments described in the present specification, the hue expressed in each pixel of the skin image is converted into an RGB vector, and modeling based on the above-described equations 1 and 2 is performed from the RGB vector. May be used to examine the basic color of the skin and the distribution of each pigment. For this purpose, the conversion module 20 may first convert the hue of each pixel of the skin image into hue data by projecting it onto the RGB log coordinate system.

  FIG. 2 is a graph showing the hue data projected on the RGB log coordinate system by the conversion module 20.

1 and 2, the conversion module 20 is formed by three coordinate axes corresponding to the three primary colors red (R), green (G), and blue (B), respectively, for the hue of each pixel of the skin image. You may project on a log coordinate system. For example, the hue of the i-th pixel in the skin image may be represented by a three-dimensional vector of [C _iR , C _iG , C _iB ], where C _iR , C _iG , and C _iB are the hues of the i-th pixel, respectively. Of these, it corresponds to red, green and blue components. A log of hue values separated into RGB is taken and converted into [log (C _iR ), log (C _iG ), log (C _iB )], and this is expressed on the RGB log coordinate system described above. When the above-described method is applied to all pixels of the skin image, hue data as shown in FIG. 2 can be obtained.

  In the hue data shown in FIG. 2, each point corresponds to the hue of one pixel of the skin image projected onto the RGB log coordinate system. In the drawings attached to this specification, the points on the RGB log coordinate system are shown in gray scale, but this does not indicate the actual hue of the pixel corresponding to each point. . Those skilled in the art will readily understand that the pixel corresponding to each point has a hue formed by combining the red, green, and blue components corresponding to the coordinates of the point in the RGB log coordinate system. Let's go.

  The first measurement module 30 may calculate the yellowness of the skin using the hue data generated by the conversion module 20. In one embodiment, the first measurement module 30 may include a basic color calculation unit 310 and a yellowness calculation unit 320. The basic color calculation unit 310 may calculate a skin basic color vector from the hue data. The basic color calculation unit 310 may arrange the illumination vector and the plurality of dye vectors whose directions are determined in advance in a polygonal pyramid shape surrounding the hue data projected on the RGB log coordinate system by the conversion module 20.

The illumination vector indicates -log (k _light ) in the above-described Expression 2. When it is assumed that white illumination that uniformly includes RGB components is used, the direction of the illumination vector may be expressed by (1, 1, 1). However, this is exemplary, and the illumination vector may have other different directions in consideration of the characteristics of the light source and / or the white balance of the camera used for skin imaging. May be configured.

The plurality of pigment vectors may be, for example, a melanin vector and a hemoglobin vector, and indicate σ _m and σ _h in Equation 2 described above. The directions of the melanin vector and the hemoglobin vector may be determined in advance using the hue data of multiple subjects. A method for extracting a melanin vector and a hemoglobin vector from an arbitrary image is well known to those skilled in the art. At this time, based on the melanin vector and the hemoglobin vector extracted from images of a large number of subjects, the embodiment of the present invention is used. The direction of the melanin vector and the hemoglobin vector used may be determined.

  For example, the directions of the melanin vector and hemoglobin vector used in the embodiments of the present invention may be determined based on the average of each of the melanin vector and hemoglobin vector extracted from the skin images of multiple subjects. Or, among melanin vectors and hemoglobin vectors extracted from skin images of a large number of subjects, a specific melanin vector that can surround hue data of a large number of subjects when arranged in the shape of a triangular pyramid together with the illumination vector described above And the direction of the hemoglobin vector.

  In this specification, a polygonal pyramid means a space surrounded by a plane formed by two of these vectors when an illumination vector and a plurality of pigment vectors are arranged at one same starting point. For example, when a plurality of pigment vectors are a melanin vector and a hemoglobin vector, a polygonal pyramid is formed by a plane formed by an illumination vector and a melanin vector, a plane formed by an illumination vector and a hemoglobin vector, and a melanin vector and a hemoglobin vector. It refers to a triangular pyramid-shaped space surrounded by three planes that are formed.

  Further, in this specification, the fact that the hue data is surrounded by a polygonal pyramid (for example, a triangular pyramid) does not necessarily mean that all the pixels of the hue data are positioned inside the polygonal pyramid. An arrangement form in which pixels of a certain ratio among all the pixels of the hue data are located inside the polygonal pyramid may be indicated. For example, the polygonal pyramid may be arranged so that about 90% or more of the pixels are located inside the polygonal pyramid, but this is illustrative and is not limited to the above numerical values.

The basic color calculation unit 310 may arrange the illumination vector, melanin vector, and hemoglobin vector whose directions are determined in advance in the form of a triangular pyramid surrounding the hue data of the subject. Referring to FIG. 2, the directions of the illumination vector, melanin vector, and hemoglobin vector are illustrated as -log (k _light ), σ _m, and σ _h , respectively. Next, the basic color calculation unit 310 may calculate -log (c _base ), which is a basic color vector representing the basic color of the subject's skin, using the position of the apex of the triangular pyramid. At this time, -log (c _base ) may be displayed at a relative position with respect to the origin of the coordinate system or a specific reference point.

On the other hand, the magnitude and / or direction of -log (c _base ), which is a basic color vector, may vary from person to person. 3a to 3c are graphs showing hue data obtained from images obtained by photographing different testers' skins. In each graph of FIGS. 3A to 3C, −log (c _base ) is the skin basic color vector of the subject, and it can be confirmed that the size and / or direction of the base color vector is different for each subject. . The difference in the basic color of the skin for each person is a phenomenon in which the general skin tone appears differently. In the present specification, this is referred to as yellowness.

The yellowness calculation unit 320 may measure the yellowness of the skin using the basic color vector calculated from the hue data by the basic color calculation unit 310. First, the yellowness calculation unit 320 can separate the basic color vector -log (c _base ) into the above-described components in the illumination vector direction and the remaining components excluding this. That is, the basic color vector separated into components in each direction can be expressed as the following Expression 3.

In Equation 3, α and β are scalar values, and γ is a vector value. (1, 1, 1) is a vector representing an illumination vector, and v _stbase is a vector representing a standard skin color obtained from a large number of subjects, which will be described in detail later.

In one embodiment, the basic color vector -log (c _base ) separated into each component as shown in Equation 3 above, except for α (1, 1, 1) that is a component in the illumination vector direction. The magnitude of the component, that is, the absolute value of _{βv stbase} + γ may be defined as skin _yellowness . For example, when the skin color vector of the subject is assumed to be (3, 4, 5), the remaining components (0, 1) are excluded except for (3, 3, 3) which is the component in the illumination vector direction. , 2) is the yellowness of the subject's skin.

In another embodiment, the remaining components of the skin basic color vector −log (c _base ) excluding α (1,1,1) which is the component in the illumination vector direction are further replaced with a predetermined standard skin color. You may isolate | separate into the component of a vector direction, and the remaining component. The standard skin color vector may be defined as the vector corresponding to the lightest color among the skin basic color vectors measured from a large number of subjects. The standard skin color vector is represented by v _stbase in Equation 3 above. According to this embodiment, among the _βv stbase + γ is the remaining ingredients except for the illumination vector directional component from the skin basic color vector, are after deducting .beta.v _Stbase is more standard skin color vector direction component The absolute value of γ is defined as yellowness. For example, as described above, in the case of a subject whose remaining component obtained by removing the component in the illumination vector direction from the skin basic color vector is (0, 1, 2), the standard skin color vector is (0, 1, 1). ), The absolute value of (0, 0, 1), which is the remainder after subtracting (0, 1, 1) from (0, 1, 2), is the yellowness of the subject's skin.

  Yellowness defined as in the above-described embodiment indicates the degree to which the hue expressed from the skin of the subject deviates from the illumination vector, and the overall color excluding the influence of the pigment in the skin color of the subject subject. A simple skin tone is expressed by a single numerical value. Therefore, by measuring the yellowness of each skin before and after use of a specific cosmetic product, there is an advantage that changes in skin tone due to product use can be easily tracked.

  On the other hand, the second measurement module 40 may calculate components of the melanin vector direction and the hemoglobin vector direction in the hue data projected onto the RGB log coordinate system by the conversion module 20. As described above, the directions of the melanin vector and the hemoglobin vector may be determined in advance using the hue data of a large number of subjects. The component in the melanin vector direction and the component in the hemoglobin vector direction calculated in this way correspond to the melanin distribution and hemoglobin distribution of the skin of the subject, respectively. The melanin distribution is expressed as skin darkness, and the hemoglobin distribution is expressed as skin redness. That is, as the amount of melanin or hemoglobin in the skin increases, the darkness or redness increases, respectively.

  In one embodiment, the skin hue measurement system displays yellowness calculated by the first measurement module 30, and melanin distribution (ie, blackness) and hemoglobin distribution (ie, redness) calculated by the second measurement module 40. An output module 50 may be included. For example, the output module 50 may display the values of skin yellowness, blackness and redness at specific positions on the coordinate system corresponding to these values. Further, the output module 50 may display the actually photographed skin image at the specific position described above.

  4A to 4C are diagrams illustrating an output form of the output module in the skin hue measurement system according to an embodiment.

  Referring to FIG. 4a, the output module may display numerical values measured from the skin of the subject on a coordinate system formed by coordinate axes corresponding to yellow, black and red, respectively. In FIG. 4a, the coordinate axes corresponding to yellow, black, and red may be set so as to illustrate a range of 0% to 200%, with the first measurement result being 100% when performing multiple measurements. . However, this is exemplary, and in other embodiments, each coordinate axis corresponding to yellow, black and red is set to illustrate, for example, a range of 90% to 110% or other different ranges. May be.

  The output module includes a first image 520 corresponding to the yellow, black and red values of the subject subject measured at a first time point (e.g., before using the cosmetic product) that is the first shooting time point, and a second time point (e.g., The second image 530 corresponding to the numerical values of yellowness, blackness and redness of the subject subject measured after using the cosmetic for a certain period of time may be displayed.

  For simplicity, only the first and second images 520 and 530 are shown in FIG. 4a. However, not only the position where the first and second images 520 and 530 are located, but also other coordinates on the coordinate system. In each place, an image corresponding to the numerical values of yellow, black, and red may be displayed. Further, such other images may be generated by adjusting yellowness, blackness and / or redness in a photographed image of an actual subject.

  The first image 520 is located on a plane 500 determined by the redness value, and similarly, the second image 530 is located on another plane 510 determined by the redness value. It becomes like this. Compared with the first time point, the redness value of the subject subject decreased at the second time point, and as a result, the second plane 510 moved closer to the direction of 0% redness than the first plane 500. Can be confirmed.

  4b is a schematic diagram illustrating only the first plane 500 in FIG. 4a, and FIG. 4c is a schematic diagram illustrating only the second plane 510 in FIG. 4a. Referring to FIGS. 4B and 4C, the first image 520 is an image taken first, so that the yellow and black values correspond to 100%, respectively, and may be displayed at the center on the first plane 500. On the other hand, the second image 530 may be displayed at a point on the second plane 510 that has moved from the center to the lower left corner because the numerical values of yellowishness and blackness are reduced as compared with the first image 520.

  For example, assuming that the red, black and yellow values of the subject subject measured at the first time point are 100%, the redness, blackness and yellowness of the subject subject measured at the second time point are 80% and 70%, respectively. % And 50%. At this time, the first image 520, which is the image of the target subject photographed at the first time point, is displayed at the position (100, 100, 100) on the coordinate system, whereas it is photographed at the second time point. The second image 530 that is an image of the subject subject can be output at a position (80, 70, 50) on the coordinate system.

  As described above, by displaying the redness, blackness and yellowness of the skin using a three-dimensional image array (array), the state of the skin may be displayed in an easy-to-understand manner. In addition, if the first time point and the second time point are set to be before and after a certain period of time after the use of a specific cosmetic product, the efficacy of the corresponding product can be visualized through a change in position from the first image 520 to the second image 530. You may grasp it. For example, the effectiveness of the product may be indicated by the length of a vector that connects a particular pixel of the first image 520 to a corresponding pixel of the second image 530. Alternatively, for each of the redness, yellowness, and blackness values, the degree of decrease in the value may be expressed in% to indicate the efficacy of the product.

  The output forms of yellowness, blackness and redness shown in FIGS. 4a to 4c are merely exemplary, and the output module is measured in the skin yellowness measured in the first measurement module and in the second measurement module. The blackness and redness of the skin may be output using another suitable display form.

  FIG. 5 is a flowchart showing a skin hue measuring method according to an embodiment.

  Referring to FIG. 5, first, the skin of the subject may be photographed as an image (S1). Next, the hue data of each pixel of the photographed skin image may be projected onto the RGB log coordinate system to generate hue data (S2). The RGB log coordinate system may be a coordinate system formed by coordinate axes corresponding to the three primary colors of red (R), green (G), and blue (B). At this time, each coordinate axis is represented by a log scale ( log scale). Each pixel of the image is represented in the form of an RGB vector in the RGB log coordinate system.

  Next, the illumination vector and the plurality of pigment vectors whose directions are determined in advance may be arranged in a polygonal pyramid (for example, a triangular pyramid) shape surrounding the projected hue data (S3). The illumination vector is a vector corresponding to the effect of illumination, and may be represented by an RGB vector of (1, 1, 1) in the case of white light. The pigment vector may be a melanin vector and a hemoglobin vector. The directions of the melanin vector and the hemoglobin vector may be determined in advance using hue data obtained from skin images of a large number of subjects.

  Next, the basic color vector may be calculated using the vertex position of the triangular pyramid composed of the illumination vector, the melanin vector, and the hemoglobin vector (S4). The basic color vector represents the skin's original general skin tone, excluding the light absorption effect due to the pigment, in the skin of the subject.

  Next, yellowness may be calculated using the basic color vector (S5). Yellowness may be obtained by dividing the basic color vector into a component in the direction of the illumination vector and a component in the remaining direction excluding this. In one embodiment, yellowness may be defined as the size of the remaining component obtained by removing the component in the illumination vector direction from the basic color vector. On the other hand, in another embodiment, yellowness is defined as the size of only the remaining components excluding the components in the predetermined standard skin color vector direction among the remaining components excluding the illumination vector direction from the basic color vector. It's okay.

  On the other hand, in the above-described hue data, a component in the melanin vector direction and a component in the hemoglobin vector direction may be calculated (S6). The component in the melanin vector direction and the component in the hemoglobin vector direction correspond to the melanin distribution and the hemoglobin distribution in the subject subject's skin, respectively. Also, the skin melanin distribution can be expressed as skin darkness, and the skin hemoglobin distribution can be expressed as skin redness.

  Next, redness, blackness, and yellowness calculated by the above-described process may be output (S7). For example, in a coordinate system formed by coordinate axes corresponding to each of redness, blackness, and yellowness, a skin image photographed at a position corresponding to the redness, blackness, and yellowness values of the subject may be output. At this time, if the image before using a specific cosmetic product and the image after a certain period of time have elapsed after use, the skin tone change due to product use can be visually confirmed through the positional change of the image before and after use. Can do.

  In the present specification, the skin hue measuring method according to one embodiment has been described with reference to the flowchart shown in the drawings. For simplicity, the method has been illustrated and described with a series of blocks, but the invention is not limited to the order of the blocks, and some blocks are described herein as others. Various other branches, flow paths, and block orders may be implemented that may occur in a different order than those illustrated and described in FIG. 1, or simultaneously, and that achieve the same or similar results. Also, not all illustrated blocks may be required to implement the methods described herein.

  The present invention described above has been described with reference to the embodiment illustrated in the drawings. However, this is merely an example, and a person having ordinary knowledge in the field may use various information. It will be understood that variations and modifications of the embodiments are possible. However, such variations should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention should be determined by the technical idea of the appended claims.

  Embodiments relate to a skin hue measurement system and method.

Claims (14)

A conversion module that converts the hue of the image of the skin image to hue data on a log coordinate system having coordinate axes corresponding to the primary colors;
A first measurement module that arranges a preset illumination vector and a plurality of pigment vectors in a polygonal pyramid shape surrounding the hue data, and measures yellow using the vertex position of the polygonal pyramid; and the hue data A skin hue measurement system comprising: a second measurement module for measuring a plurality of pigment distributions by separating the illumination vector component into the illumination vector component and the pigment vector component.   The skin hue measurement system according to claim 1, wherein the plurality of pigment vectors include a melanin vector and a hemoglobin vector. The first measurement module includes:
A basic hue calculation unit that calculates a basic color vector corresponding to a vertex position of the polygonal pyramid from the hue data; and the basic color vector except for the component in the illumination vector direction and the component in the illumination vector direction. The skin hue measurement system according to claim 1, further comprising a yellowness calculation unit that calculates yellowness by separating into components.   The skin hue measurement system according to claim 3, wherein the yellow corresponds to a remaining component of the basic color vector excluding a component in the illumination vector direction. The yellowness calculating unit removes the remaining components of the basic color vector excluding the components of the illumination vector direction from the components of the preset standard skin color vector direction and the components of the standard skin color vector direction. Separated into the ingredients of
The yellow color corresponds to a remaining component of the basic color vector excluding a component in the standard skin color vector direction from a remaining component excluding the component in the illumination vector direction. 4. The skin hue measurement system according to 3.   An output for displaying yellowness calculated in the first measurement module and a plurality of pigment distributions calculated in the second measurement module on a coordinate system having coordinate axes corresponding to yellowness and the plurality of pigment distributions, respectively. The skin hue measurement system according to claim 1, further comprising a module.   The skin color measurement system according to claim 6, wherein the output module displays an image obtained by photographing the skin on a coordinate system having coordinate axes corresponding to the yellowness and a plurality of pigment distributions. . Converting the hue of an image obtained by photographing the skin into hue data on a log coordinate system having coordinate axes corresponding to primary colors;
Arranging a preset illumination vector and a plurality of pigment vectors in a polygonal pyramid shape surrounding the hue data;
Measuring yellow using the apex position of the polygonal pyramid; and measuring the plurality of pigment distributions by separating the hue data into components in the illumination vector direction and components in the pigment vector directions A method for measuring skin hue, comprising a step.   The skin hue measurement method according to claim 8, wherein the plurality of pigment vectors include a melanin vector and a hemoglobin vector. The step of measuring the yellowness of the skin comprises
Calculating a basic color vector corresponding to a vertex position of the polygonal pyramid from the hue data; and separating the basic color vector into the remaining components excluding the illumination vector direction component and the illumination vector direction component. The method for measuring skin hue according to claim 8, further comprising a step of calculating yellowing.   11. The skin hue measuring method according to claim 10, wherein the yellow corresponds to a remaining component of the basic color vector excluding a component in the illumination vector direction. The step of calculating the yellowness includes excluding a component in the standard skin color vector direction and a component in the standard skin color vector direction that are set in advance from the remaining components of the basic color vector except for the component in the illumination vector direction. And separating the remaining ingredients,
The yellow color corresponds to a remaining component of the basic color vector excluding a component in the standard skin color vector direction from a remaining component excluding the component in the illumination vector direction. 10. The method for measuring skin hue according to 10.   The method of claim 8, further comprising displaying the calculated yellowness and the plurality of pigment distributions on a coordinate system having coordinate axes corresponding to the yellowness and the plurality of pigment distributions, respectively. Skin hue measurement method.   The step of displaying on the coordinate system having coordinate axes corresponding to each of the yellowness and the plurality of pigment distributions displays an image obtained by photographing the skin at a position corresponding to the calculated yellowness and the plurality of pigment distributions. The method according to claim 13, further comprising a step.

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