JP6401091B2 - Optical simulation apparatus and method, and program - Google Patents

Description

  The present invention relates to an optical simulation apparatus, method, and program for generating and displaying an image of an object by simulation based on the optical characteristics of the object.

  It is important to scientifically image and analyze changes in physical properties of objects. For example, elucidating the relationship between the physical properties of skin and how it looks is important in the fields of cosmetics and dermatology.

  As a method for evaluating the appearance of the skin as described above, it has been proposed to generate and display a skin image by simulation. For example, Patent Document 1 proposes that a skin image is generated and displayed by setting optical characteristics for a skin model obtained by modeling the skin and simulating the luminance distribution of the skin model. Patent Documents 2 to 4 propose using a CG (Computer Graphics) model to generate and display a simulation image representing skin texture, pores, and the like.

JP 2014-73333 A JP 2011-161105 A JP 2013-196172 A JP 2014-120005 A Japanese Patent Laid-Open No. 8-17885

  Here, a Monte Carlo method is known as a method generally used when performing a simulation (see, for example, Patent Document 5). The Monte Carlo method is a calculation method for obtaining an approximate solution of an event from the results of trials of observing an output value by each variable many times using a pseudo random number for an event that can be represented by a random variable.

  For example, when a distribution as shown in FIG. 19 with d as a variable is simulated by the Monte Carlo method, a method using a probability distribution type table and a method using an intensity distribution type table can be considered. Table 1 below shows the distribution shown in FIG. 17 as a probability distribution type table.

Here, for example, consider the case of simulating the intensity distribution of light emitted from a light source. When the sum of the intensities of the light beams emitted from the light source is 1, and the simulation is performed with 100 light beams, the intensity per one light beam is 0.01. Then, when 10 light beams are assigned to each of the 10 tables shown in Table 1 and a random number of 1 to 10 is generated and a simulation is performed, the intensity distribution of the light beams emitted from the light source is shown in FIG. The intensity distribution is as shown in FIG.

  On the other hand, as a method for realizing the intensity distribution as shown in FIG. 17, there is a method using an intensity distribution table. The intensity distribution type table is a table of variable values and corresponding intensity distributions. Table 2 below shows the distribution of FIG. 19 using an intensity distribution type table.

Even when a simulation is performed by generating random numbers corresponding to the variable d (−4 to 5) using the table in Table 2, an intensity distribution as shown in FIG. 19 can be obtained.

  Here, for example, when the sampling interval of the variable d is made fine to increase the accuracy of the intensity distribution, in the method using the probability distribution type table described above, the number of tables increases as the sampling interval becomes fine. Therefore, there is a problem that the capacity of a storage medium such as a memory for storing the table becomes insufficient. In other words, if the memory capacity is constant, the resolution of the table becomes insufficient if the sampling interval of the variable is made fine.

  Specifically, for example, when the distribution as shown in FIG. 20 is represented by a probability distribution type table, when normalized so that the total sum of distributions is 1 as described above, the minimum probability is 0.025 units. Become. If an attempt is made to create a table with 10 tables, the resolution of the table is 0.1, so it is not possible to express 0.1 units or less.

  On the other hand, when the distribution shown in FIG. 20 is represented by an intensity distribution type table, it can be represented by the following table 3. That is, it can be represented by 0.025 units, but half of the table has a light intensity of 0. In addition, there is a problem in that it takes a long calculation time because it is necessary to refer to all tables of 0 values in the simulation.

When simulating the optical characteristics of an object such as skin, for example, when simulating a distribution with a large number of variables such as BSSRDF (Bidirectional Scattering Surface Reflectance Distribution Function) characteristics and a wide range of variables, as described above. If a probability distribution type table is used, the accuracy of the simulation cannot be increased because the number of tables is limited. On the other hand, if an intensity distribution type table is used, useless calculations increase and the calculation cost increases.

  In view of the above problems, an object of the present invention is to provide an optical simulation apparatus, method, and program capable of suppressing calculation cost and simulating emitted light from an object with high accuracy.

  An optical simulation apparatus of the present invention includes an optical characteristic acquisition unit that acquires an optical characteristic of an object, a table conversion unit that converts the optical characteristic into a table set in which a probability distribution type table and an intensity distribution type table are combined, and an object A surface shape information acquisition unit that acquires information on the surface shape of the object, and a simulation unit that simulates light emitted from the object based on the information on the surface shape and the table set.

  Here, the “optical property of the object” may be an optical property obtained by directly measuring the object, or may be an optical property obtained by analyzing a mathematical model of the object by simulation. .

  Further, the optical simulation apparatus of the present invention includes an image generation unit that forms an image by forming an image of the emitted light by the simulation, and a display control unit that displays the image generated by the image generation unit on the display unit. Can do.

  In the optical simulation apparatus of the present invention, the optical property acquisition unit can acquire the bidirectional scattering surface reflectance distribution function of the object as the optical property.

  In the optical simulation apparatus of the present invention, the table conversion unit converts the distribution of the emission position defined by the bidirectional scattering surface reflectance distribution function into a probability distribution type table, and the bidirectional scattering surface reflectance distribution function Can be converted into an intensity distribution type table.

  In the optical simulation apparatus of the present invention, the table conversion unit converts the distribution of emission positions defined by the bidirectional scattering surface reflectance distribution function into an intensity distribution type table, and the bidirectional scattering surface reflectance distribution function. Can be converted into a probability distribution type table.

  In the optical simulation apparatus of the present invention, the optical property acquisition unit can acquire the bidirectional scattering distribution function of the object as the optical property.

  In the optical simulation device of the present invention, the table conversion unit converts the distribution of the first emission angle that specifies the emission direction defined by the bidirectional scattering distribution function into a probability distribution type table, and converts the emission direction to the probability distribution type table. The distribution of the second emission angle different from the identified first emission angle can be converted into an intensity distribution type table.

  In the optical simulation apparatus of the present invention, the table conversion unit converts the distribution of the first emission angle that specifies the emission direction defined by the bidirectional scattering distribution function into an intensity distribution type table, and converts the emission direction into the intensity distribution type table. The distribution of the second emission angle different from the identified first emission angle can be converted into a probability distribution type table.

  In the optical simulation apparatus of the present invention, the optical property acquisition unit can acquire the bidirectional reflectance distribution function of the object as the optical property.

  In the optical simulation apparatus of the present invention, the table conversion unit converts the distribution of the first emission angle specifying the emission direction defined by the bidirectional reflectance distribution function into a probability distribution type table, and the emission direction. It is possible to convert the distribution of the second emission angle different from the first emission angle specifying the angle into an intensity distribution type table.

  In the optical simulation apparatus of the present invention, the table conversion unit converts the distribution of the first emission angle that specifies the emission direction defined by the bidirectional reflectance distribution function into an intensity distribution table, and the emission direction. It is possible to convert the distribution of the second emission angle different from the first emission angle that specifies the probability distribution type table.

  In the optical simulation apparatus of the present invention, the object is preferably skin.

  In the optical simulation apparatus of the present invention, a skin surface characteristic calculation unit that calculates an electric field distribution of the skin surface model by analyzing a skin surface model obtained by modeling the skin surface structure using electromagnetic field optics, A skin internal property calculation unit that calculates the light scattering characteristics of the skin internal model by analyzing the internal skin model that models the internal structure using geometric optics, and the skin surface model based on the electric field distribution of the skin surface model An optical characteristic calculation unit that calculates an optical characteristic and combines the optical characteristic of the skin surface model and the light scattering characteristic of the internal skin model to calculate the optical characteristic of the entire skin, and the optical characteristic acquisition unit includes the optical characteristic The optical characteristics of the entire skin calculated by the calculation unit can be acquired.

  In the optical simulation apparatus of the present invention, the optical characteristic acquisition unit can acquire optical characteristics obtained by actually measuring an object.

  In the optical simulation apparatus of the present invention, the image generation unit can receive the setting of the target area and allow the emitted light from the object to enter only the target area when performing the simulation.

  The optical simulation method of the present invention acquires the optical characteristics of an object, converts the optical characteristics into a table set combining a probability distribution type table and an intensity distribution type table, and acquires information on the surface shape of the object. The light emitted from the object is simulated based on the surface shape information and the table set.

  An optical simulation program of the present invention includes an optical characteristic acquisition unit that acquires an optical characteristic of an object, a table conversion unit that converts the optical characteristic into a table set in which a probability distribution type table and an intensity distribution type table are combined, and an object The computer is caused to function as a simulation unit for simulating the light emitted from the object based on the surface shape information acquisition unit for acquiring the surface shape information and the surface shape information and the table set.

  According to the optical simulation apparatus, method, and program of the present invention, an optical characteristic of an object is acquired, and the optical characteristic is converted into a table set in which a probability distribution type table and an intensity distribution type table are combined. Then, information on the surface shape of the object is acquired, and light emitted from the object is simulated based on the information on the surface shape and the table set described above. In other words, calculation costs can be reduced by performing some simulations using probability distribution tables, and high-precision simulations can be performed by performing some simulations using intensity distribution tables. Can do. As a result, the calculation cost can be suppressed, and the emitted light from the object can be simulated with high accuracy.

The block diagram which shows schematic structure of the skin simulation image display system using one Embodiment of the optical simulation apparatus of this invention Illustration for explaining BSSRDF characteristics Diagram for explaining BSDF (Bidirectional Scattering Distribution Function) characteristics, BRDF (Bidirectional Reflectance Distribution Function) characteristics, BTDF (Bidirectional Transmittance Distribution Function characteristics) and BSDF (Bidirectional Scattering Distribution Function) characteristics A diagram representing the light intensity in the emission direction (φr, ψr) at each emission position (ur, vr) when the incident direction φi = 0 ° as a three-dimensional graph. A diagram representing the light intensity in the emission direction (φr, ψr) at each emission position (ur, vr) when the incident direction φi = 30 ° as a three-dimensional graph. The figure which shows an example of the uneven | corrugated shape of a texture The figure which shows an example of the uneven | corrugated shape of a pore The figure for demonstrating the generation method of the skin image by simulation The flowchart for demonstrating the effect | action of the skin simulation image display system using one Embodiment of the optical simulation apparatus of this invention. The block diagram which shows other embodiment of an optical characteristic acquisition part. The figure which shows an example of the skin surface model which arranged the several sphere The figure which shows the other example of the skin surface model which arranged the plurality of spheres The figure which shows an example of the skin surface model which laminated | stacked the layered structure The figure which shows an example of the skin surface model supposing the skin where the stratum corneum is arranged Diagram showing BSDF characteristics when light is incident from 0 ° to a skin surface model that assumes rough skin Diagram showing BSDF characteristics when light is incident from 0 ° to a skin surface model that assumes a well-organized skin. The figure which showed the calculation method of the optical characteristic of the whole skin typically The figure which showed typically the calculation method of the optical characteristic of the whole skin at the time of comprising a skin internal model from two or more layers Diagram showing an example of simulation distribution Diagram showing another example of simulation distribution

  Hereinafter, a skin simulation image display system using an optical simulation apparatus and method and a program according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a skin simulation image display system 1 of the present embodiment. The configuration of the optical simulation apparatus shown in FIG. 1 is realized by installing an embodiment of the optical simulation program of the present invention in a computer and executing the program by the computer. The optical simulation program installed in the computer may be stored in a recording medium such as a CD-ROM (Compact Disc Read Only Memory), or may be distributed via a network such as the Internet.

  As shown in FIG. 1, the skin simulation image display system 1 of this embodiment includes an optical simulation device 10, a display device 20, and an input device 30.

  The optical simulation device 10 includes an optical property acquisition unit 11, a table conversion unit 12, a surface shape information acquisition unit 13, a simulation unit 14, an image generation unit 15, and a display control unit 16.

  The optical property acquisition unit 11 acquires the optical property of the object. Specifically, the optical characteristic acquisition unit 11 of the present embodiment acquires the optical characteristic of the skin.

  The skin optical characteristics define the light reflection characteristics, transmission characteristics, scattering characteristics, and the like when light is incident on the skin. The optical characteristics of the skin may be obtained by actually measuring the actual skin, or may be obtained by analyzing a skin model obtained by modeling the skin by simulation. The skin model is a mathematical model of human skin, and is obtained by setting skin structure information, light refractive index, scattering coefficient, absorption coefficient, and the like. The skin model may be set in advance, or may be set by the user inputting optical information such as the above-described structure information and refractive index using the input device 30.

  Specifically, the optical characteristics include BSSRDF (Bidirectional Scattering Reflectance Distribution Function) characteristics, BSDF (Bidirectional Scattering Distribution Function) characteristics and SVBRDF (Spatially Varying Bidirectional Reflectance Distribution Function) (both (Directional reflectance distribution function) characteristics. These optical characteristics are already known, but will be briefly described below.

  The BSSRDF characteristic represents the reflection characteristic of the object surface. As shown in FIG. 2I, light incident on an arbitrary position on the object surface is scattered inside the object and emitted from another position on the object surface. It is taken into consideration. As shown in FIGS. 2II and 2III, the BSSRDF characteristic is obtained by using the incident position (ui, vi) and the incident direction (φi, ψi) as inputs, and the emission position (ur, vr) and the emission as shown in FIGS. 2IV and 2V. It is given by the distribution output in the direction (φr, ψr).

  The BSDF characteristic is a combination of a BRDF characteristic (Bidirectional Reflectance Distribution Function) and a BTDF (Bidirectional Transmittance Distribution Function) characteristic.

  As shown in FIG. 3I, the BRDF characteristic represents the reflection characteristic of the object surface, and is given by a distribution output in the emission direction (φr, ψr) with the incident direction (φi, ψi) as an input. As shown in FIG. 3II, the BTDF characteristic represents the transmission characteristic of the object surface, and is given by a distribution output in the emission direction (φr, ψr) with the incident direction (φi, ψi) as an input. That is, the BSDF characteristic is also given by a distribution output in the emission direction (φr, ψr) with the incident direction (φi, ψi) as an input.

  The optical characteristics of the skin acquired by the optical characteristics acquisition unit 11 may be set in advance, or may be arbitrarily set and input by the user using the input device 30. Further, a plurality of optical characteristics may be set in advance, and the user may select from among the plurality of optical characteristics using the input device 30. Regarding the selection of the optical characteristics, for example, a selection screen may be displayed on the display device 20, and the user may select a desired optical characteristic on the selection screen. As the plurality of optical characteristics, different optical characteristics such as BSSRDF characteristics, BSDF characteristics, and BRDF characteristics may be set. For example, for the BSSRDF characteristics, a plurality of BSSRDF characteristics having different optical characteristics may be set. May be.

  The table conversion unit 12 converts the optical characteristics of the skin acquired by the optical characteristic acquisition unit 11 into a table set combining a probability distribution type table and an intensity distribution type table.

  Specifically, for example, when the optical characteristic is a BSSRDF characteristic, the distribution of the emission position (ur, vr) described above is converted into a probability distribution type table and corresponds to each emission position (ur, vr). The distribution in the emission direction (φr, ψr) is converted into an intensity distribution type table. Conversely, the distribution of the emission position (ur, vr) is converted into an intensity distribution type table, and the distribution of the emission direction (φr, ψr) corresponding to each emission position (ur, vr) is converted to a probability distribution type. It may be converted into the table.

  Further, when the optical characteristics are BSDF characteristics and BRDF characteristics, the distribution of the emission direction (φr) described above is converted into a probability distribution type table, and the emission direction (ψr) corresponding to each emission direction (φr) is converted. ) Distribution is converted into an intensity distribution type table. Conversely, the distribution of the emission direction (φr) is converted into an intensity distribution type table, and the distribution of the emission direction (φr) corresponding to each emission direction (φr) is converted into a probability distribution type table. Also good.

  Here, a method for converting the BSSRFD characteristics described above into a table set of a probability distribution type table and an intensity distribution type table will be specifically described. As described above, the BSSRDF characteristic is a distribution that is output in the emission position (ur, vr) and the emission direction (φr, ψr) with the incident position (ui, vi) and the incident direction (φi, ψi) as inputs. Here, in order to make the explanation easy to understand, the optical characteristics are not changed depending on the incident position (ui, vi) and the incident direction ψi, that is, considering only the incident direction φi, the incident direction φi is set to 0 ° to The case of 30 ° increments in the 30 ° range is considered. Further, the emission position (ur, vr) is set to 1 mm in the range of −1 to 1 mm in the x direction and the y direction, the emission direction φr is set to 15 ° in the range of 0 ° to 90 °, and the emission direction ψr is set to 0 °. The case where it is set in increments of 60 ° in a range of ˜360 ° shall be considered. From the definition as described above, the BSSRDF characteristic here is the four-dimensional distribution of the emission position (ur, vr) and the emission direction (φr, ψr) when the incident direction φi = 0 °, and the incident direction φi = 30. It is given by the four-dimensional distribution of the emission position (ur, vr) and the emission direction (φr, ψr) at °.

  Specifically, the emission position (ur, vr) when the incident direction φi = 0 ° can be expressed by a distribution as shown in Table 4 below, for example. Further, the light intensity in each emission direction (φr, ψr) at each emission position (ur, vr) can be expressed by a distribution as shown in Table 5 below, for example. FIG. 4 shows the light intensity in the emission direction (φr, ψr) at each emission position (ur, vr) as a three-dimensional graph.

Further, the emission position (ur, vr) when the incident direction φi = 30 ° can be expressed by a distribution as shown in Table 6 below, for example. Further, the light intensity in each emission direction (φr, ψr) at each emission position (ur, vr) can be represented by a distribution as shown in Table 7 below, for example. FIG. 5 is a three-dimensional graph showing the light intensity in each emission direction (φr, ψr) at each emission position (ur, vr).

Next, using the distributions in Tables 4 and 5, the distribution of the emission position (ur, vr) when the incident direction φi = 0 ° is converted into a probability distribution type table. Specifically, when the distribution of light intensity in each emission direction (φr, ψr) at each emission position (ur, vr) in Table 5 is added, the distribution shown in Table 8 below is obtained. That is, for example, when all the intensity distributions in the respective emission directions (φr, ψr) of (ur, vr) = (− 1, 1) in Table 5 are added, (ur, vr) = (− 1, 1) in Table 8 The value is 2.060887. Further, when all the intensity distributions in the emission directions (φr, ψr) of (ur, vr) = (0, 0) in Table 5 are added, the value of (ur, vr) = (0, 0) in Table 8 is obtained. There will be 8.476945.

Then, the sum of all the values in Table 8 is obtained, and each value in Table 8 is divided by the sum to obtain the probability, and the values up to the second decimal place are as shown in Table 9 below.

Probability of Table 9 is obtained by tabulating the number of 10 ^second table is a table on the left of Table 10 below. This table is obtained by converting the distribution of emission positions (ur, vr) when the incident direction φi = 0 ° into a probability distribution type table. The left table of Table 10 is a table in which the probability distribution of the emission positions (ur, vr) is represented by random numbers from 1 to 100.

  The right table of Table 10 is a table in which the distribution of the emission position (ur, vr) when the incident direction φi = 30 ° is converted into a probability distribution type table in the same manner as in the case of the incident direction φi = 0 °. It is.

Next, the light intensity distribution in each emission direction (φr, ψr) corresponding to each emission position (ur, vr) is converted into an intensity distribution type table. For this intensity distribution type table, the distributions represented by Tables 6 and 7 may be tabulated as they are. In this intensity distribution table, a predetermined emission direction (φr, ψr) is determined by using the emission direction (φr, ψr) as a random number, and the intensity of the determined emission direction (φr, ψr) is determined.

  In the above description, the distribution of the emission position (ur, vr) is converted into a probability distribution table, and the distribution of the emission direction (φr, ψr) corresponding to each emission position (ur, vr) is expressed as an intensity distribution. As described above, the case of converting to a table of molds has been explained. Conversely, the distribution of emission positions (ur, vr) is converted to an intensity distribution type table to correspond to each emission position (ur, vr). The distribution in the outgoing direction (φr, ψr) may be converted into a probability distribution type table.

As a method for converting the distribution of the emission direction (φr, ψr) into a probability distribution type table, specifically, for each emission direction (φr, ψr), the distribution of the light intensity at each emission position is added. Then, a light intensity distribution is calculated such that ur, vr in Table 8 is replaced with φr, ψr. Then, by dividing the added value of the light intensity for each emission direction (φr, ψr) by the sum of the added values, a probability distribution such that ur, vr in Table 9 is replaced with φr, ψr is calculated. . Then, it is sufficient to convert a probability distribution type table by tabulating the number of tables that probability example 10 ^2.

  As described above, when the optical characteristic is the BSDF characteristic or the BRDF characteristic, the distribution of the emission direction (φr) is converted into a probability distribution type table, and the emission direction corresponding to each emission direction (φr) ( The distribution of ψr) is converted into an intensity distribution type table, or conversely, the distribution of the emission direction (φr) is converted into an intensity distribution type table, and the emission direction (ψr) corresponding to each emission direction (φr) is converted. ) Distribution may be converted into a probability distribution type table, but as a conversion method to the table, basically, the same method as in the BSSRFD characteristic described above may be used.

  The surface shape information acquisition unit 13 acquires information on the surface shape of the skin. The information on the surface shape of the skin may be information obtained by actually measuring the actual skin, or information on the surface shape of the skin model obtained by modeling the skin. As the information on the surface shape of the skin model, for example, a flat surface assuming smooth skin may be used, or an uneven surface assuming pores and unevenness on the skin surface may be used. FIG. 6 shows an example of a textured uneven shape, and FIG. 7 shows an example of an uneven shape of a pore. As the size of the unevenness, for example, an unevenness of micrometer order to millimeter order is set. Specifically, the surface shape information is given by three-dimensional coordinates (x, y, z). Further, when generating a skin image, which will be described later, the normal vector (Nx, Ny, Nz) of each point is calculated from the three-dimensional coordinates.

  Information on the surface shape of the skin acquired by the surface shape information acquisition unit 13 may be set in advance, or may be arbitrarily set and input by the user using the input device 30. Alternatively, a plurality of surface shapes may be set in advance, and the user may select from among the plurality of surface shapes using the input device 30. As for the selection of the surface shape, for example, a selection screen may be displayed on the display device 20, and the user may select a desired surface shape on the selection screen.

  The simulation unit 14 is based on a table set including a probability distribution type table and an intensity distribution type table generated by the table conversion unit 12, and information on the skin surface shape acquired by the surface shape information acquisition unit 13. Simulates light emitted from the skin. The probability distribution type table is, for example, the table shown in Table 10 above, and the intensity distribution type table is, for example, the tables shown in Table 6 and Table 7.

  The image generation unit 15 forms an image by forming an image of the emitted light by the simulation in the simulation unit 14.

  In generating a skin image, first, as shown in FIG. 8, a light source 100, a skin model 101, a condenser lens 102, and a light receiving unit 103 are set in a simulation space. Then, the parallel light L1 emitted from the light source 100 is incident on the skin model 101, and the emitted light L2 emitted from the skin model 101 due to the incidence of the parallel light L1 is condensed by the condenser lens 102. By calculating until the light is received by the light receiving surface, a skin image formed on the light receiving surface of the light receiving unit 103 can be simulated. As simulation conditions, for example, a 20 mm square is set as the size of the light emitting surface of the light source 100, a 20 mm square is set as the size of the light incident surface of the skin model 101, and a radius of 15 mm is set as the size of the condenser lens 102. The distance between the skin model 101 and the condenser lens 102 is set to 500 mm, and the distance between the condenser lens 102 and the light receiving unit 103 is set to 140 mm.

  More specifically, the parallel light L1 is emitted from the light source 100 many times. The incident position of each light beam is determined by geometrically calculating the position when each light beam of the parallel light L1 reaches the surface of the skin model 101. Next, for each ray, the incident direction of each ray is determined by considering the direction of the ray and the normal vector of the surface shape of the skin model 101. Then, by referring to the table set generated by the table conversion unit 12 based on the incident position and incident direction of each light ray, the emission position, emission direction and intensity of each light ray emitted from the skin model 101 Is determined. Specifically, in the above-described example, the emission position of each ray of the emitted light is determined by referring to the probability distribution type table, and the emission direction and intensity are determined by referring to the intensity distribution type table. A skin image is generated by forming each light beam of the emitted light transmitted through the condenser lens 102 on the light receiving surface of the light receiving unit 103.

  When determining the light emission direction, the light emission direction may be determined so that the light is incident only on a preset target area. For example, the area of the condenser lens 102 may be set as the target area. The target area can be arbitrarily set by the user using the input device 30.

  For example, when the optical characteristics of the skin model 101 are BSDF characteristics or BRDF characteristics, the skin model 101 is referred to by referring to the table set generated by the table conversion unit 12 based on the incident direction of each ray of incident light. The emission direction and intensity of each ray of the emitted light emitted from the model 101 are determined. Specifically, for example, the emission direction φr of each ray of the emitted light is determined by referring to the probability distribution type table, and the emission direction ψr and the intensity corresponding to the emission direction φr are determined by referring to the intensity distribution type table. Is done. Note that, as described above, conversely, the emission direction ψr of each ray of the emitted light is determined by referring to the probability distribution type table, and the emission direction φr corresponding to the emission direction ψr by referring to the intensity distribution type table. And the strength may be determined.

  The display control unit 16 causes the display device 20 to display the skin image generated by the image generation unit 15.

  The display device 20 includes a monitor such as a liquid crystal display. The display device 20 may be a tablet terminal monitor. That is, an optical simulation program may be installed on the tablet terminal to display a skin image.

  The input device 30 includes a keyboard and a mouse for receiving input of various information such as information on the optical characteristics of the skin and the surface shape of the skin, and simulation conditions. Moreover, you may make it serve as both the display apparatus 20 and the input device 30 with the touch panel of the tablet terminal mentioned above.

  Next, the effect | action of the skin simulation image display system 1 of this embodiment is demonstrated, referring the flowchart shown in FIG.

  First, skin optical characteristics such as BSSRDF characteristics, BSDF characteristics, and BRDF characteristics are acquired by the optical characteristic acquisition unit 11 (S10).

  Then, the optical characteristics of the skin are output to the table conversion unit 12, and the table conversion unit 12 converts the input optical characteristics into a table set including the probability distribution type table and the intensity distribution type table as described above. (S12).

  On the other hand, information on the surface shape of the skin is acquired by the surface shape information acquisition unit 13 (S14). Then, the table set generated in the table conversion unit 12 and the information on the surface shape of the skin acquired by the surface shape information acquisition unit 13 are output to the simulation unit 14.

  As described above, the simulation unit 14 refers to the table set generated by the table conversion unit 12 based on the incident direction and the incident position of each light ray determined based on the information on the surface shape of the skin. The emission position, emission direction, and intensity of each light beam emitted from the model are determined. Then, the image generation unit 15 generates a skin image in which each light ray of the simulated emitted light is imaged on the light receiving surface (S16).

  The skin image generated by the image generation unit 15 is output to the display control unit 16, and the display control unit 16 causes the display device 20 to display the input skin image (S18).

  According to the skin simulation image display system 1 of the above embodiment, the optical characteristics of an object are acquired, and the optical characteristics are converted into a table set in which a probability distribution type table and an intensity distribution type table are combined. Then, information on the surface shape of the object is acquired, and based on the information on the surface shape and the table set described above, the light emitted from the object is imaged by simulation to generate an image, and the image is displayed. Therefore, the calculation cost can be suppressed and an image can be generated and displayed by a highly accurate optical simulation.

  In the above embodiment, the optical characteristic acquisition unit 11 acquires BSSRDF characteristics, BSDF characteristics, and BRDF characteristics as the optical characteristics of the skin. However, the optical characteristic acquisition unit 11 sets a skin model, and the skin The BSSRDF characteristic may be calculated by simulation by analyzing the model. Hereinafter, a specific example in which the optical property acquisition unit 11 calculates the BSSRDF property by simulation will be described. Here, the skin surface model and internal skin model are set as the skin model, the skin surface model is analyzed using electromagnetic field optics, and the internal skin model is analyzed using geometric optics, so that the BSSRDF characteristics of the entire skin are analyzed. A method for calculating the value will be described. By this method, it is possible to calculate BSSRDF characteristics obtained by more strictly analyzing the surface structure of the skin surface model. Thereby, the change in the microstructure of the skin surface can be estimated with high accuracy, and the subtle changes in the texture of the skin due to the change in the microstructure can be evaluated.

  Specifically, as shown in FIG. 10, the optical property acquisition unit 11 includes a skin surface property calculation unit 50 and a skin internal property calculation unit 51.

  The skin surface characteristic calculation unit 50 calculates an electric field distribution of the skin surface model by analyzing a skin surface model obtained by modeling the skin surface structure using electromagnetic field optics. The skin surface model may be generated in the skin surface characteristic calculation unit 50 based on information such as the shape and refractive index of the skin input by the user using the input device 30, or a skin surface model generated in advance. May be stored in the skin surface characteristic calculation unit 50.

  As the skin surface model, for example, a skin surface model obtained by modeling skin having a surface microstructure that assumes rough skin such as peeling of the stratum corneum can be used. The micro structure here is a structure of 10 micrometers or less, and is a structure finer than the above-described unevenness information of the skin surface shape. Specifically, for example, a structure in which a plurality of spheres having random diameters in the range of 200 nm to 800 nm are arranged can be used as the skin surface model. As a method for arranging the spheres, for example, 55 spheres may be arranged at random positions within a range of 5 μm square.

  FIG. 11 is a diagram illustrating an example of a skin surface model that assumes rough skin. In addition, the arrangement method may be an arrangement having regularity. The size, density, and arrangement method of the spheres can be arbitrarily changed by the user using the input device 30. FIG. 12 shows the sphere density smaller than that of the skin surface model shown in FIG.

  In this embodiment, a sphere is used. However, the structure is not limited to a sphere, and other structures such as a cylinder, a cone, and a polyhedron may be arranged. Further, a plurality of these types of structures may be set in advance so that the user can arbitrarily select them using the input device 30. Moreover, you may make it mix not only one type but multiple types of structures.

  Further, the skin surface model may be generated from a structure other than a sphere. For example, as shown in FIG. 13, a layered structure may be stacked and generated. The skin surface model shown in FIG. 13 is considered to be a model closer to the actual stratum corneum. In addition, when a plurality of layered structures are stacked, the shape of each layer may be different. The shape of each layer may be arbitrarily set by the user. Moreover, you may produce | generate the uneven | corrugated shape of a surface using the index value (for example, arithmetic mean roughness Ra) etc. of surface roughness.

  Further, as the skin surface model, a model obtained by modeling the surface structure of the skin that is moisturized and the stratum corneum is arranged may be used. In this case, a skin surface model having a flat structure with no irregularities may be used. FIG. 14 is a diagram illustrating an example of a skin surface model assuming skin with a well-organized stratum corneum. Further, the refractive index of the skin surface model may be set to n = 1.37, which is generally known as the refractive index of the skin, for example. Further, assuming that sebum covers the surface of the stratum corneum, the refractive index of sebum may be set to about n = 1.5.

  It is desirable to generate or store in advance a skin surface model that assumes a plurality of skin conditions, such as a skin surface model that assumes rough skin as described above, or a skin surface model that assumes skin with a well-organized stratum corneum. The user can select a skin surface model to be analyzed from the plurality of skin surface models as necessary. In this case, a menu for selecting the skin surface model to be analyzed from the plurality of skin surface models is displayed on the display device 20, and the user uses the input device 30 from the menu display to analyze the skin surface model to be analyzed. May be selected.

  The skin surface characteristic calculation unit 50 analyzes the skin surface model as described above using electromagnetic field optics. Specifically, the spatial distribution of the electromagnetic field in the reflection direction and the transmission direction when light is incident on the skin surface model having a spatial distribution of refractive index (dielectric constant) is calculated. For example, the analysis may be performed using the FDTD method (Finite-difference time-domain method). The FDTD method is a method of calculating the temporal change of the spatial distribution of the electromagnetic field by directly differentiating the Maxwell equation. However, not limited to the FDTD method, for example, a finite element method, a boundary element method, and other generally known electromagnetic field calculation methods can be used.

  In addition, when analyzing using electromagnetic field optics, if a periodic boundary condition is used, a skin area model of a wide mm order is virtually analyzed using a skin surface model of a finite size (for example, 5 μm square unit). be able to. Thereby, calculation cost can be suppressed.

  Further, data to be discretized by analysis using a skin surface model having a finite size (for example, 5 μm square unit) may be continuously handled by interpolation. Thereby, calculation cost can be suppressed.

  Next, the internal skin characteristic calculation unit 51 calculates the light scattering characteristics of the internal skin model by analyzing the internal skin model that models the internal structure of the skin using geometric optics.

  The skin internal model has a macro structure larger than the skin surface model, and the macro structure here may be a structure having a size relatively larger than the uneven structure of the skin surface model, and is 10 micrometers. A larger uneven structure or a flat structure may be used. The skin internal model may be generated by estimating an optical constant inside the skin by a known method such as evaluation using slit light and setting a scattering coefficient and an absorption coefficient for each wavelength.

  The internal skin characteristic calculation unit 51 analyzes the internal skin model as described above using geometric optics. Specifically, in this embodiment, the scattering coefficient μs, the absorption coefficient μa, and the anisotropic scattering coefficient g are set as the characteristics of the skin internal model (scattering body), and random numbers are used according to the setting of the scattering coefficient μs. The distance until the light beam is scattered is obtained, and the light goes straight. Then, the next traveling direction of the scattered light is determined using a random number. The probability distribution in the traveling direction is given based on the probability distribution of the Henyey-Greenstein scattering function shown in the following equation.

Then, the attenuation of the amount of light accompanying the propagation of the light beam is given by the absorption coefficient μa. The above process is repeated to calculate, and the propagation characteristics of light that is multiply scattered in the skin internal model (scattering body) are calculated as the light scattering characteristics of the skin internal model. Note that g = 0.9, which is generally used as the skin coefficient, may be used as the anisotropic scattering coefficient g.

  The optical characteristic calculation unit 52 calculates the optical characteristics of the skin surface model based on the electric field distribution of the skin surface model calculated by the skin surface characteristic calculation unit 50, and calculates the calculated optical characteristics and internal skin characteristics of the skin surface model. The optical characteristics of the entire skin are calculated by combining the light scattering characteristics of the skin internal model calculated by the unit 51.

  The optical characteristic calculator 52 first calculates a light scattering angle distribution based on the electric field distribution of the skin surface model. Specifically, in the present embodiment, a BSDF (Bidirectional Scattering Distribution Function) of the skin surface model is calculated based on the electric field distribution of the skin surface model. Hereinafter, the BSDF calculation method will be described more specifically.

  In the calculation result by the FDTD method in the skin surface characteristic calculation unit 50, the periodic structure becomes a diffraction grating, and light is transmitted or reflected at a specific emission angle determined by the diffraction order. In addition, the periodic structure here is a structure in which, for example, in the example of the skin surface model described above, a unit structure is a 5 μm square region in which spheres are randomly arranged, and this unit structure is repeatedly arranged in a plane. is there.

  Assuming that the polar coordinate display of the incident angle of light is (θ0, φ0) and the wavelength of light is λ, wave number vectors kx0, ky0 in the x and y directions are expressed by the following equations.

When the diffraction orders in the x and y directions are m and n, and the period length is L, the wave numbers kxm and kyn of the diffracted light in the x and y directions are expressed by the following equations.

The scattering angles (θmn, φmn) of the mth and nth order diffracted light can be calculated by the following equations.

Next, the light quantity of each diffraction order can be calculated by the following method from the calculation result of the FDTD method.

  Let E (x, y) be the spatial distribution of the electric field on one surface of the given x, y plane obtained from the calculation result of the FDTD method. Further, the electric field distribution obtained by correcting the phase change depending on the incident angle of the incident light with respect to E (x, y) is calculated as E ′ (x, y) by the following equation.

Then, E ′ (x, y) is Fourier-transformed as in the following equation, and the amplitude E (m, n) of the electric field of diffraction orders m and n is calculated.

The amount of light of the diffraction order m, n can be calculated as Imn = | E (m, n) | ² .

With the above calculation, the calculation result by the FDTD method can be converted into the angular distribution of scattered light, and the conversion result can be acquired as BSDF of the skin surface model. As BSDF, BSDF (f) in the case of surface incidence in which light is incident on the skin from the air layer and BSDF (b) in case of light incident on the air layer from the inside of the skin are calculated. FIG. 15 is a diagram showing BSDF when light is incident from a direction of 0 ° with respect to a skin surface model that assumes rough skin, and FIG. 16 shows a skin surface model that assumes skin with a well-organized stratum corneum. It is a figure showing BSDF when light injects from a 0 degree direction. The size of one pixel in FIGS. 15 and 16 is 200 mm ⁻¹ .

  Then, the optical characteristic calculation unit 52 adds the BSDF of the skin surface model calculated as described above to the light scattering characteristic of the skin internal model calculated by the skin internal characteristic calculation unit 51, thereby providing the entire skin. BSSRDF characteristics are calculated as the optical characteristics. FIG. 17 schematically shows a method for calculating the optical characteristics of the entire skin in the optical characteristic calculator 52. As a result, the optical properties of the entire skin can be handled with geometric optics.

  In the above embodiment, the skin internal model has a single layer structure. However, the present invention is not limited to this, and the skin internal model may be formed of a plurality of layers as shown in FIG. When the skin internal model is composed of a plurality of layers, optical constants such as a scattering coefficient and an absorption coefficient may be set for each layer. For example, the scattering coefficient and the absorption coefficient may be set assuming the skin layer and the dermis layer. Specific values of optical constants such as a scattering coefficient and an absorption coefficient are previously measured by experiments or the like.

  When the skin internal model is composed of an epidermis layer and a dermis layer, an uneven shape assuming a dermal papillary layer may be set at the boundary between the epidermis layer and the dermis layer. In the example shown in FIG. 18, the internal skin model is composed of two layers, but three or more layers may be used. For example, “Reproduction of skin disease and spectral reflectance analysis using multilayer skin phantom, 2012 Nippon Optics As shown in “Annual Academic Lecture, Proceedings”, an internal skin model may be composed of nine layers. By constructing the skin internal model from a large number of layers in this way, it is possible to obtain a configuration closer to actual skin.

  In the above description, the skin model is set, and the skin model is analyzed by simulation to calculate the optical characteristics of the skin. However, the actual optical characteristics of the skin are measured without using the skin model. Then, the optical characteristic acquisition unit 11 may acquire the actually measured optical characteristic.

  As a method for actually measuring the BRDF characteristics of the skin, first, light is incident on the actual skin, and the incident direction of the light is stored. Light emitted from the skin by the incidence of light on the skin is received by the sensor, and the emission direction and intensity of the emitted light are stored. Then, the BRDF characteristics may be calculated from the incident direction of the incident light, the emission direction of the emitted light, and the intensity. As a method for actually measuring the BRDF characteristics, for example, the methods described in JP-A-2009-162516 and JP-T-2008-539439 can be used.

  The BSSRDF characteristic can be measured by using a turtle shell polygon mirror set to distribute light in 48 directions by a polyhedral mirror arranged in a hemisphere, for example. Specifically, light is incident on actual skin and the incident position and direction of the light are stored. The light emitted from the skin by the light incident on the skin is distributed by the turtle shell polygon mirror. The distributed reflected light is imaged by a camera to form an image, and the intensity of the reflected light having a spread at the exit position is measured for each exit direction. Then, the BSSRDF characteristic may be calculated from the incident position, incident direction, outgoing position, outgoing direction, and intensity of reflected light of incident light. In addition, the measurement method of BSSRDF characteristics using a turtle shell polygon mirror is, for example, “CHIKA INOSHITA et al.,“ Full-dimensional Sampling and Analysis of BSSRDF ”, IPSJ Transaction on Computer Vision and Application Vol.5 119-123 (July 2013)” It is described in.

DESCRIPTION OF SYMBOLS 1 Skin simulation image display system 10 Optical simulation apparatus 11 Optical characteristic acquisition part 12 Table conversion part 13 Surface shape information acquisition part 14 Simulation part 15 Image generation part 16 Display control part 20 Display apparatus 30 Input device 50 Skin surface characteristic calculation part 51 Skin Internal characteristic calculation unit 52 Optical characteristic calculation unit 100 Light source 101 Skin model 102 Condensing lens 103 Light receiving unit

Claims (17)

An optical property acquisition unit for acquiring the optical property of the object;
A table conversion unit that converts the optical characteristics into a table set combining a probability distribution type table and an intensity distribution type table;
A surface shape information acquisition unit for acquiring information on the surface shape of the object;
An optical simulation apparatus comprising: a simulation unit that simulates light emitted from the object based on the surface shape information and the table set. An image generation unit that forms an image by imaging the emitted light by the simulation; and
The optical simulation apparatus according to claim 1, further comprising: a display control unit that causes the display unit to display an image generated by the image generation unit.   The optical simulation apparatus according to claim 1, wherein the optical property acquisition unit acquires a bidirectional scattering surface reflectance distribution function of the object as the optical property.   The table conversion unit converts the distribution of emission positions defined by the bidirectional scattering surface reflectance distribution function into a probability distribution type table, and the distribution in the emission direction defined by the bidirectional scattering surface reflectance distribution function. The optical simulation apparatus according to claim 3, wherein the light is converted into an intensity distribution table.   The table conversion unit converts the distribution of the emission position defined by the bidirectional scattering surface reflectance distribution function into an intensity distribution type table, and the distribution in the emission direction defined by the bidirectional scattering surface reflectance distribution function. The optical simulation apparatus according to claim 3, wherein the table is converted into a probability distribution type table.   The optical simulation apparatus according to claim 1, wherein the optical property acquisition unit acquires a bidirectional scattering distribution function of the object as the optical property. The table conversion unit converts the distribution of the first emission angle specifying the emission direction defined by the bidirectional scattering distribution function into a probability distribution type table, and the first emission angle specifying the emission direction is The optical simulation apparatus according to claim 6, wherein the distribution of different second emission angles is converted into an intensity distribution type table. The table conversion unit converts a first emission angle distribution that specifies an emission direction defined by the bidirectional scattering distribution function into an intensity distribution type table, and the first emission angle that specifies the emission direction is The optical simulation apparatus according to claim 6, wherein the distribution of different second emission angles is converted into a probability distribution table.   The optical simulation apparatus according to claim 1, wherein the optical property acquisition unit acquires a bidirectional reflectance distribution function of the object as the optical property. The table conversion unit converts the distribution of the first emission angle that specifies the emission direction defined by the bidirectional reflectance distribution function into a probability distribution type table, and the first emission angle that specifies the emission direction ; The optical simulation apparatus according to claim 9, wherein the distribution of different second emission angles is converted into an intensity distribution type table. The table conversion unit converts the distribution of the first emission angle that specifies the emission direction defined by the bidirectional reflectance distribution function into an intensity distribution type table, and the first emission angle that specifies the emission direction ; The optical simulation apparatus according to claim 9, wherein the distribution of different second emission angles is converted into a probability distribution type table.   The optical simulation apparatus according to claim 1, wherein the object is skin. A skin surface property calculation unit that calculates an electric field distribution of the skin surface model by analyzing a skin surface model that models the surface structure of the skin using electromagnetic field optics;
An internal skin property calculation unit that calculates the light scattering characteristics of the internal skin model by analyzing the internal skin model that models the internal structure of the skin using geometric optics; and
The optical characteristics of the skin surface model are calculated based on the electric field distribution of the skin surface model, and the optical characteristics of the entire skin are calculated by combining the optical characteristics of the skin surface model and the light scattering characteristics of the skin internal model. And an optical property calculation unit
The optical simulation apparatus according to claim 12, wherein the optical characteristic acquisition unit acquires the optical characteristics of the entire skin calculated by the optical characteristic calculation unit.   The optical simulation apparatus according to claim 1, wherein the optical characteristic acquisition unit acquires optical characteristics obtained by actually measuring the object. The optical simulation apparatus according to claim 2 , wherein when the image generation unit receives a setting of a target area and performs the simulation, light emitted from the object is incident only on the target area. Get the optical properties of the object,
Converting the optical characteristics into a table set combining a probability distribution type table and an intensity distribution type table;
Obtaining information on the surface shape of the object;
An optical simulation method comprising simulating light emitted from the object based on the surface shape information and the table set. An optical property acquisition unit for acquiring the optical property of the object;
A table conversion unit that converts the optical characteristics into a table set combining a probability distribution type table and an intensity distribution type table;
A surface shape information acquisition unit for acquiring information on the surface shape of the object;
An optical simulation program that causes a computer to function as a simulation unit that simulates light emitted from the object based on the surface shape information and the table set.