JP2022119427A - Calculation device, calculation method, and program - Google Patents

Abstract

To provide a calculation device that, when reproducing a state in which an object including luminous material is coated by CG, can efficiently represent a luminous feel with a small amount of calculation even from a macro point of view.SOLUTION: A calculation device comprises: an acquisition unit that acquires object shape information indicating the shape of an object, coating information indicating the number of luminous materials included in the predetermined area and the degree of distribution of subsurface normals of the luminous materials, and luminous material information indicating the reflection characteristics on the luminous materials; a subsurface normal calculation unit that calculates the subsurface normals of the luminous materials included in the predetermined area by using the degree of distribution of the subsurface normals and the object shape information; and a reflectance calculation unit that, by using the luminous material information and the subsurface normals calculated by the subsurface normal calculation unit, calculates the reflectance of the luminous materials with a light source and a line-of-sight direction as variables according to a viewpoint distance from a viewpoint position of a camera to the object.SELECTED DRAWING: Figure 1

Description

The present invention relates to a computing device, computing method and program. In particular, the present invention relates to a technique for expressing the display color of an object containing glittering materials by computer graphics.

In the automobile industry, image representation by computer graphics (hereinafter referred to as CG) is often used in advertisements, promotions, and design stages. Painted panels, which make up the majority of the exterior of automobiles, have been tried to accurately express with CG due to their complicated construction. Many coated plates are composed of multiple layers, and by containing flake pigments in the layers, the flakes have a glittering effect (granularity: flakes give a crushing feeling) and flip-flop properties that change the color depending on the viewing angle. It has a reflection characteristic of If such reflection characteristics can be accurately represented by CG, it will be unnecessary to actually apply paint to the object to check the finish at the design stage.

Japanese Patent Laid-Open No. 2002-200002 discloses a technique for measuring the angular spectral reflectance and reproducing the paint color of an object by CG. In this technique, since CG is generated using the measured declination spectral reflectance, it is possible to express the flip-flop nature of the painted surface in which the color changes depending on the viewing angle.

Several reflection models have been proposed to express the feeling of glitter caused by flakes. For example, in Non-Patent Document 1, the appearance of a coated plate is represented by a uniform Bidirectional Reflectance Distribution Function (BRDF) due to pigments and a BTF (Bidirectional Texture Function) that changes depending on the coordinate position. BTF is a method of expressing appearance with an image, and is a method of storing and reproducing changes in appearance due to differences in light source and line-of-sight direction as an image. Flakes are also expressed by saving the appearance when viewed from a certain direction as an image.

Also, in a Car Paint shader (reflection model) provided by a 3DCG software development company as shown in Non-Patent Document 2, calculations are made for each of the clear coat layer, the flake layer, and the pigment layer expressing diffuse reflection. In the flake layer, a rough brilliance is expressed by scaling a normal map texture generated by random numbers.

Further, in Non-Patent Document 3, the number of flakes included in the coated plate is formulated as a normal distribution under the surface of the coated plate. By calculating the gloss from a plurality of normals expressed by the normal distribution, it is possible to express the feeling of glitter due to a plurality of flakes present in one pixel of the texture.

JP-A-10-115555

M. Rump, G. Muller, R. Sarlette, D. Koch and R. Klein, “Photo-realistic Rendering of Metallic Car Paint from Image-Based Measurements”, Computer Graphics Forum, Vol. 27-2, pp.527- 536 (2008). [online], “Car Paint Material / Shader”, [searched on January 29, 2021], Internet <URL: https://knowledge.autodesk.com/support/3ds-max/learn-explore/caas/ CloudHelp/cloudhelp/2015/ENU/3DSMax/files/GUID-1CD21856-588A-4A05-AC0A-88489F5F9C84-htm.html>. Sho Ikemoto, Yasuhiro Mukaigawa, Yasuyuki Matsushita, Hiroyuki Kubo, Yasushi Yagi, "Analysis of subsurface normal distribution of metallic paint considering observation scale", Information Processing Society of Japan research report, CG-161-15, (2015).

However, the expression of flip-flop properties alone as described in Patent Literature 1 is insufficient for the expression of coated plates, and the expression of luster by flakes is important. In Non-Patent Document 1, a huge number of images are required in order to smoothly express the change in brightness due to the change in viewpoint position. In Non-Patent Document 2, one flake exists for one pixel of the texture. For this reason, it is difficult to express a change in brightness due to a change in viewpoint position. Non-Patent Document 3 focuses on the quantification of the feeling of brightness, and does not mention a CG generation method using this.

When trying to express the feeling of brightness by flakes, it is necessary to express the change in appearance according to the viewpoint distance. Since the method of Non-Patent Document 1 is an image-based method, it is difficult to express the feeling of brilliance because the effect of the flakes is crushed from a macro viewpoint away from the coated plate. Conversely, from a microscopic point of view close to the coated plate, texture resolution is low, and it is difficult to finely express flakes of about 20 [μm].

In the shader of Non-Patent Document 2, the flake attenuation distance can be set in order to eliminate the sense of incongruity due to flake expression from a macro viewpoint. This is a process of gradually fading out the influence of flakes by the set viewpoint distance. However, since the influence of flakes exists even from a macroscopic point of view, it is difficult to say that this is a correct expression.

Therefore, as described in Non-Patent Document 3, by defining the number of normal lines under the surface per certain area and calculating the reflected light from there, the feeling of glitter due to flakes can be obtained from both micro and macro viewpoints. can be expressed. However, since the rendering resolution is low in the macro viewpoint, the area corresponding to one pixel in the coated plate area becomes large, and the number of subsurface normals included in one pixel becomes enormous. Representing all of this huge number of subsurface normals would require a huge amount of computational time.

The present invention has been made in view of such circumstances. The present invention provides a computing device and calculation that can efficiently express a feeling of glitter with a small amount of calculation even from a macro viewpoint when reproducing a painted state of an object containing a glitter material by CG. It aims at providing a method and a program.

In order to solve the above problems, a computing device according to an embodiment of the present invention is a computing device that calculates the display color of an image that expresses the feeling of glitter in an object containing a glittering material by computer graphics, and calculates the shape of the object. light source information indicating a light source that illuminates the object; camera information related to a camera that virtually captures the object; the number of glittering materials contained in a predetermined area; and the acquisition unit for acquiring painting information indicating the degree of distribution of and luster material information indicating the reflection characteristics of the luster material; a sub-surface normal calculation unit that calculates the sub-surface normal of the glittering material, and the above-mentioned glittering material information and the sub-surface normal calculated by the sub-surface normal calculation unit, the light source and the line-of-sight direction are changed to variables A reflectance calculation unit that calculates the reflectance of the glitter material according to the viewpoint distance from the viewpoint position of the camera to the object; and the glitter material drawn in the drawing pixels using the reflectance calculated by the reflectance calculation unit, the incident light calculated by the incident light calculation unit, and the camera information. and the reflected light components calculated by the specular reflected light calculation unit are added for the number of the glitter materials included in the drawing pixel, and the display of the drawing pixel is performed. and an output unit configured to output the display color for each pixel calculated by the brightness addition unit.

In order to solve the above problems, the calculation method of the embodiment of the invention is a calculation method performed by a computer device for calculating the display color of an image that expresses the feeling of glitter in an object containing a glitter material by computer graphics. The section includes object shape information indicating the shape of the object, light source information indicating the light source that illuminates the object, camera information related to a camera that virtually captures the object, the number of the glittering materials contained in a predetermined area, and the glittering Painting information indicating the degree of distribution of the normal under the surface of each material and luster material information indicating the reflection characteristics of the luster material are acquired, and the sub-surface normal calculation unit calculates the distribution degree of the sub-surface normal and Using the object shape information, the normal under the surface of the glittering material included in the predetermined area is calculated, and the reflectance calculation unit calculates the normal under the surface calculated by the glittering material information and the normal under the surface Using the normal line, the reflectance of the glitter material with the light source and line-of-sight direction as variables is calculated according to the viewpoint distance from the viewpoint position of the camera to the object, and the incident light calculation unit calculates the light source information. is used to calculate the incident light for the drawing pixel to be drawn, and the specular reflected light calculation unit calculates the reflectance calculated by the reflectance calculation unit, the incident light calculated by the incident light calculation unit, and the Using the camera information, the reflected light component of the glittering material to be drawn in the drawing pixel is calculated, and the brightness adding unit includes the reflected light component calculated by the specular reflection light calculating unit in the drawing pixel. The display color of the drawing pixel is calculated by adding up the number of the glittering materials, and the output unit outputs the display color for each pixel calculated by the glitter adding unit.

In order to solve the above problems, a program according to an embodiment of the present invention provides a computer device that calculates the display color of an image that expresses the feeling of glitter in an object containing a glitter material by computer graphics. shape information, light source information indicating a light source that illuminates the object, camera information related to a camera that virtually captures the object, the number of the glittering materials contained in a predetermined area, and the distribution of the normals under the surface of each of the glittering materials an acquisition step of acquiring painting information indicating the degree of luster and luster material information indicating a reflection characteristic of the luster material; The subsurface normal calculation step of calculating the subsurface normal of the luster material with the light source and the line of sight direction as variables a reflectance calculation step of calculating the reflectance of according to the viewpoint distance from the viewpoint position of the camera to the object; calculating a reflected light component of the glittering material to be drawn on the drawing pixels using the calculating step, the reflectance calculated by the reflectance calculating step, the incident light calculated by the incident light calculating step, and the camera information; a specular reflected light calculation step for calculating a display color of the drawn pixel by adding the reflected light components calculated by the specular reflected light calculation step by the number of the glitter materials included in the drawn pixel; and an output step of outputting the display color for each pixel calculated by the brightness addition step.

According to the embodiment of the present invention, when reproducing a painted state of an object containing a glittering material by CG, it is possible to express the feeling of glittering efficiently with a small amount of calculation even from a macro viewpoint. can.

1 is a block diagram showing a configuration example of a display device 1 of an embodiment; FIG. FIG. 2 is a schematic diagram showing coating containing glittering material of the embodiment. It is a figure which shows the structural example of the coating information 121 of embodiment. It is a figure which shows the structural example of the glitter material information 122 of embodiment. It is a figure which shows the structural example of the light source information camera information 123 of embodiment. It is a figure used for description of the process which the reflectance calculation part 132 of embodiment performs. FIG. 4 is a diagram showing an example of reflection lobes by the glittering material of the embodiment; 4 is a flowchart showing the flow of processing performed by the display device 1 of the embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The display device 1 is, for example, a computer device such as a PC (Personal Computer) or a server device. The display device 1 generates an image in which the display color of an object containing a glittering material is drawn using a computer graphics technique, and displays the generated image. The display device 1 is an example of a “computing device”.

In the following, a case of drawing an object coated with a coating agent containing a luster material will be described as an example. However, it is not limited to painting. Any object that contains at least a luster material can be used. For example, the present invention can be applied to drawing an object manufactured by forming a substance into which a luster material is kneaded.

FIG. 1 is a block diagram showing a configuration example of a display device 1 according to an embodiment. The display device 1 includes, for example, a communication section 11, a storage section 12, a control section 13, and a CG display section . The communication unit 11 is implemented by, for example, a general-purpose communication IC (Integrated Circuit). The communication unit 11 communicates with an external device via, for example, the Internet communication network, receives information transmitted from the external device, and stores the received information in the storage unit 12 .

The storage unit 12 is implemented by, for example, a storage device (a storage device having a non-transitory storage medium) such as a HDD (Hard Disk Drive) or flash memory, or a combination thereof. The storage unit 12 stores a program for realizing each component of the display device 1, variables used when executing the program, and various kinds of information.

The storage unit 12 stores object shape information 120, painting information 121, glitter material information 122, and light source information camera information 123, for example. The object shape information 120 is information indicating the three-dimensional shape of an object. The object shape information 120 is, for example, data indicating the polygonal shape of a virtual object created by CAD (Computer-Aided Design) or the like, and includes surface normal information of each polygon. The painting information 121 is information indicating the state of painting. The painting information 121 includes, for example, information indicating the state of distribution of the luster material contained in the painting for each kind of painting to be drawn. The light source information camera information 123 is information of a virtual light source used for drawing and a virtual camera that captures an image of an object.

Here, the relationship between the coating 20 and the luster material 21 included in the coating 20 will be described with reference to FIG. FIG. 2 is a schematic diagram showing coating containing the glitter material of the embodiment.

In general, an object has only one normal and one reflection peak at one point. However, as shown in FIG. 2, in an object such as the coating 20 containing the luster material 21, the normal line _n0 of the surface of the coating 20 is determined as one, but the reflection due to the effect of the luster material 21 existing under the surface There are multiple peaks. Therefore, in the present embodiment, the normal line _nsi by the bright material 21 existing under the surface is defined as the normal line under the surface. However, i is a number according to the number of glittering materials.

FIG. 2 shows an example in which four luster materials 21-1 to 21-4 are included in the coating 20 having a predetermined area defined by the side lengths (Δx, Δy). The normal to the surface of the coating 20 is normal _n0 . The normal line under the surface of the glitter material 21-1 included in the paint 20 is the normal line n _s1 under the surface. The subsurface normal to the bright material 21-2 is the subsurface normal n _s2 . The subsurface normal to the bright material 21-3 is the subsurface normal n _s3 . The subsurface normal to the glitter 21-4 is the subsurface normal n _s4 .

FIG. 3 is a diagram showing a configuration example of the painting information 121 of the embodiment. The painting information 121 includes, for example, items such as "Painting No.", "Side length x", "Side length y", "Glitter material number", and "Normal dispersion". "Coating No." is identification information that uniquely identifies a coating. “Side length x” and “side length y” are information indicating the length of one side and the length of the other side when defining the area of the coating 20 . “Number of glittering materials” is information indicating the number of glittering materials 21 included in a predetermined area defined by “side length x” and “side length y”. The normal dispersion is information (dispersion information) indicating the state of dispersion of normals under the surface due to ^each bright material 21, and is information indicating dispersion s2, for example. where s is the standard deviation of the subsurface normal due to each glitter 21 .

In the example of this figure, the paint No. It is shown that the coating 20 identified by 1 includes N ₁ glitter materials 21 within a predetermined area of side length (Δx ₁ , Δy ₁ ). It is also shown that the dispersion of the subsurface normals by each of the N ₁ glittering materials 21 is S ₁ ² .

FIG. 4 is a diagram showing a configuration example of the glitter material information 122 of the embodiment. The glittering material information 122 includes items such as, for example, "gliting material No.", "specular reflection coefficient", and "surface roughness". "Glittering Material No." is identification information that uniquely identifies a glittering material. The "specular reflection coefficient" and "surface roughness" are parameters when the luster material is a specular reflection model indicating specular reflection. In the example of this figure, glitter material No. The glitter 21 identified by ₁ is shown to have a specular reflection coefficient of k _s1 and a surface roughness of σ ¹² .

FIG. 5 is a diagram showing a configuration example of the light source information camera information 123 according to the embodiment. The light source information camera information 123 is, for example, information set by the user or information stored in advance. The light source information camera information 123 includes items such as “No.”, “light source information”, and “camera information”, for example. "No." is identification information that uniquely identifies a combination of light source information and camera information. The light source information is information about a virtual light source used for drawing, and is, for example, information indicating the position of the light source in the world coordinate system and the intensity of the light source. The camera information is information about a virtual camera used for drawing, and is, for example, information indicating the position of the camera in the world coordinate system, the angle of view of the camera, the number of pixels during rendering, and the like. In the example of this figure, No. The light source information identified by 1 indicates that the position coordinates of the light source are P _L1 (x _L1 , y _L1 , z _L1 ) and the intensity of the light source is I _L1 . Also, No. 1, the camera position coordinates are P _c1 (x _c1 , y _c1 , z _c1 ), the camera angle of view is (θ _x1 , θ _y1 ), and the number of pixels is (U ₁ , V ₁ ).

Returning to the description of FIG. 1 , the control unit 13 stores processing units such as a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit) as hardware included in the display device 1 in the storage unit 12. Functions are realized by executing the program.

The control unit 13 includes, for example, an acquisition unit 130, a subsurface normal calculation unit 131, a reflectance calculation unit 132, an incident light calculation unit 133, a specular reflection light calculation unit 134, a brightness addition unit 135, Prepare.

The acquisition unit 130 acquires various information necessary for drawing. Specifically, the acquisition unit 130 acquires object shape information 120 , painting information 121 , glitter material information 122 , and light source information camera information 123 . The acquisition unit 130 outputs the acquired information to the subsurface normal calculation unit 131 . Practically speaking, the acquisition unit 130 outputs the object shape information 120 to the subsurface normal calculation unit 131 .

Here, processing performed by the subsurface normal calculation unit 131 will be described with reference to FIG. 6A and 6B are diagrams used for explaining the processing performed by the subsurface normal calculation unit 131. FIG. FIG. 6 schematically shows a state in which the luster material is distributed in each of the micro viewpoint and the macro viewpoint.

The subsurface normal calculation unit 131 calculates subsurface normals. The subsurface normal calculation unit 131 acquires the object shape information 120 from the acquisition unit 130, and acquires the normal _n0 of the polygon corresponding to the pixel to be drawn based on the acquired information. Further, the subsurface normal calculation unit 131 obtains the painting information 121 from the obtaining unit 130, and obtains dispersion information indicating variations in the subsurface normal of the paint to be drawn based on the obtained information.

In the painting information 121, as dispersion information, for example, the degree of dispersion around the normal _n0 direction of the surface of the painting ²⁰ is indicated by dispersion s2. In this case, the subsurface normal calculation unit 131 calculates the zenith angle of each subsurface normal using a normal distribution Nd(0, s ² ) with an average of 0 (zero) and a variance of s ² . do. In addition, the subsurface normal calculation unit 131 obtains the azimuth angle of the subsurface normal using, for example, a uniform random number. In this way, the subsurface normal calculator 131 determines the subsurface normal vector n _s of each of the glitter 21 by calculating the zenith angle and the azimuth angle.

The reflectance calculator 132 calculates the reflectance of one glitter material 21 . The reflectance calculator 132 reads and acquires the position coordinates of pixels to be drawn (hereinafter referred to as drawing pixels) from the object shape information 120 . The reflectance calculation unit 132 acquires the position coordinates of the light source and the camera used for drawing from the light source information camera information 123 . The reflectance calculation unit 132 derives a light source direction vector l and a line-of-sight direction vector v for a drawing pixel using the position coordinates of the drawing pixel, the light source, and the camera. In addition, the reflectance calculation unit 132 acquires the subsurface normal vector n _s calculated by the subsurface normal calculation unit 131, the specular reflection coefficient ks of the coating read from the glitter material information 122, and the surface roughness σ ² . do. The reflectance calculator 132 calculates the reflectance of the glitter material 21 using the acquired information.

Here, in this embodiment, the viewpoint distance is taken into consideration when calculating the reflectance of the glitter material 21 . The viewpoint distance is the distance from the viewpoint position of the camera to the object to be drawn. The reflectance calculation unit 132 controls the resolution at the time of rendering to an appropriate resolution according to the viewpoint distance. The method by which the reflectance calculator 132 calculates the reflectance of the glitter material 21 in consideration of the viewpoint distance will be described with reference to FIG.

FIG. 6 is a diagram used for explaining the processing performed by the reflectance calculation unit 132 of the embodiment. FIG. 6 schematically shows the outline of the glitter material distribution from micro and macro viewpoints. When perspective projection is considered during rendering (drawing), the positional relationship of the camera 30, window 31, and view volume 32 is as shown in FIG.

When focusing on one pixel existing in the window 31, the drawing range 33 at the micro viewpoint, that is, when the object is close to the camera 30, is very small. In this case, the number of glitter material images 330 to be drawn contained in the small drawing range 33 is reduced. On the other hand, the rendering range 34 is large at a macro viewpoint, that is, when the object is far from the camera. In this case, the number of glitter material images 340 to be drawn contained in the large drawing range 34 increases.

The drawing area S of one pixel in the window 31 can be obtained from the angle of view of the camera, the number of pixels, and the distance d. A distance d is the distance (viewpoint distance) from the camera 30 to the drawing range 34 . The painting information 121 also stores a predetermined area ΔS consisting of side lengths (Δx, Δy) and the number N of glittering materials contained in the predetermined area. From this, the number of glittering materials included in the drawing range can be obtained by N×S/ΔS. Here, N is the number of glittering materials included in the predetermined area ΔS. S is the drawing area. ΔS is a predetermined area.

Here, the particle size per one glitter material is about 20 [μm], which is very small. Therefore, in the macro viewpoint, the number of glittering materials 21 existing in the rendering range corresponding to one pixel becomes enormous. Therefore, it takes a very long time to calculate the reflectance of each of the glittering materials 21 .

By the way, when a coated plate containing the luster material 21 is observed from a macro viewpoint, the reflected light from each of the plurality of luster materials 21 is mixed, and the reflected light having a large spread is felt. There is Therefore, using this property, in the present embodiment, the sum of reflected light from a plurality of glittering materials is approximately calculated based on the reflection characteristics from one glittering material 21 . Specifically, the characteristics obtained by widening the reflection lobe indicated by the reflection characteristics of one glitter material 21 are approximately expressed as the reflection characteristics of a plurality of glitter materials.

Here, a method for approximately representing the sum of reflected light from a plurality of glittering materials will be described with reference to FIG. FIG. 7 is a diagram showing reflection lobes (radiance characteristics of reflected light) by the glitter material of the embodiment. The horizontal axis in FIG. 7 indicates the line-of-sight angle, and the vertical axis indicates the radiance.

In FIG. 7, the illumination is incident perpendicularly to the surface of the glitter material 21, that is, from the normal direction of the surface. Therefore, the reflectance of the glitter material 21 changes depending on the line-of-sight angle, and the radiance of the reflected light also changes accordingly.

A reflection lobe due to a single (one) glitter material 21 has a sharp peak as indicated by the solid line in FIG. When observing from a viewpoint distance (distance d1) such that only one image of the glittering material to be drawn is included in the drawing range indicated by one pixel in the window 31, the glittering material Brilliance is expressed as a characteristic having a sharp peak as indicated by the solid line in FIG.

On the other hand, consider a case where an object including the luster material 21 having the same reflection characteristics is observed from a viewpoint distance (referred to as a distance d2) that is twice the distance d1. When observed from the distance d2, the drawing range indicated by one pixel in the window 31 includes four images of the glitter material to be drawn. Here, when the rendering range is considered to be one-dimensional, the feeling of glitter is expressed as a characteristic obtained by synthesizing the respective reflection characteristics from two glitter materials.

In this embodiment, instead of calculating the reflectance of each of the two glittering materials 21, the reflection characteristics of the two glittering materials 21 double the spread of the reflection lobe due to a single glittering material 21. approximation is assumed to be the characteristics of Specifically, it is assumed that the reflection characteristics of the two glittering materials 21 are reflection lobes having gentle peaks as indicated by broken lines in FIG.

Consider the Ward model as an example of the specular reflection model. The reflectance ρ _s in the Ward model is obtained by the following equation (1) using the light source/line-of-sight direction vector (l, v) as a variable. In equation (1), σ is the surface roughness coefficient and ks is the specular reflection coefficient. Also, α is the angle formed by the subsurface normal vector n _s and the half vector. A half vector is a unit vector representing an intermediate direction of the light source/line-of-sight direction vector (l, v). is a vector.

Based on equation (1), the Ward model determines the width of the reflection lobe so as to be proportional to the surface roughness σ. Therefore, when it is desired to double the width of the reflection lobe, the reflectance calculation unit 132 calculates the surface roughness σ′ when the width of the reflection lobe is doubled as the surface roughness of the original glitter material 21. It should be twice the roughness σ.

Specifically, when using the approximation described above, the reflectance calculator 132 calculates the surface roughness σ′ by the following equation (2). In equation (2), S is the area of the drawing range corresponding to one pixel. ΔS is a predetermined area defined by the side length (x, y) stored in the painting information 121 . σ is the surface roughness of the glitter material 21 stored in the glitter material information 122 .

Also, the reflectance calculator 132 calculates the specular reflection coefficient ks' by the following equation (3). In equation (3), S is the area of the drawing range corresponding to one pixel. ΔS is a predetermined area defined by the side length (x, y) stored in the painting information 121 . ks is the specular reflection coefficient of the glitter material 21 stored in the glitter material information 122 .

FIG. 7 shows an example of a reflection lobe by one bright material. When drawing, each reflectance is calculated according to the number of glittering materials 21 included in the predetermined area ΔS indicated in the coating information 121 . For example, when four glittering materials 21 are included in the predetermined area ΔS and the drawing area S corresponds to the predetermined area ΔS, the reflectance of each of the four glittering materials 21 is calculated as before. . In this case, if the drawing area S corresponds to 10 times the predetermined area ΔS, conventionally, it is necessary to calculate the reflectance of each of the 40 glittering materials 21 . On the other hand, in the present embodiment, one glittering material (hereinafter referred to as an integrated glittering material) corresponding to (S/ΔS=) ten glittering materials 21 is considered, and the reflectance by the integrated glittering material is approximately calculate. Then, assuming that the drawing area S includes four integrated glitter materials, the reflectance of each integrated glitter material is calculated (approximately).

Specifically, the reflectance calculator 132 uses the approximate surface roughness σ′ obtained by the equation (2) and the approximate specular reflection coefficient ks′ obtained by the equation (3) to obtain an approximate Calculate reflectance. As a result, the reflectance calculation unit 132 does not repeat calculations for synthesizing the reflection characteristics of a huge number of glittering materials 21 from the macro viewpoint, but performs a plurality of The reflectance of the glitter material can be approximately calculated. Therefore, even from a macro viewpoint, it is possible to approximate the feeling of brightness without increasing the calculation time.

Returning to the description of FIG. 1, the incident light calculator 133 calculates incident light. The incident light calculator 133 acquires the position coordinates (coordinate data P _O ) of the drawing pixels from the object shape information 120 . The incident light calculator 133 acquires the position coordinates of the light source (light source coordinate position P _L ) and the intensity of the light source (light source intensity I _L ) used for drawing from the light source information camera information 123 . The incident light calculator 133 also obtains the subsurface normal vector n _s calculated by the subsurface normal calculator 131 . The incident light calculator 133 uses the acquired information to calculate the irradiance Ei of light incident on the glitter material 21 under the surface of the object from the light source. For example, when the light source is a point light source, the incident light calculator 133 calculates the light irradiance Ei using the following equation (4). In equation (4), Ei is the light _irradiance and IL is the light source intensity. Also, _dL is the distance between the light source and the pixel, and _θi is the angle between the normal vector ns under the surface of the luster material 21 to be drawn and the incident light.

The specular reflected light calculation unit 134 calculates the reflected light component of the specular surface of the glitter material 21 included in the drawing pixel. The specular reflected light calculator 134 multiplies the reflectance ρ _s by the irradiance Ei to calculate the radiance I _s from the glitter material 21 as a reflected light component. The specular reflected light calculator 134 uses the value calculated by the reflectance calculator 132 as the reflectance _ρs . The specular reflected light calculator 134 uses the value calculated by the incident light calculator 133 as the irradiance Ei.

The glitter adding unit 135 synthesizes the glitter by the glitter material 21 included in the drawing pixel. Specifically, the glitter adding unit 135 calculates the sum of the reflected light components (radiance I _s ) of the N glittering materials 21 included in the predetermined area ΔS in the painting 20 to be drawn. This is the display color of the pixel that expresses painting.

As a result, regardless of the size of the drawing area S, all the pixels that express the painting express a feeling of brilliance that includes the respective reflected light components (radiance I _s ) of the N luminous materials 21. It will happen. Moreover, since the approximation is such that the width of the reflection lobe of the glittering material 21 increases as the size of the drawing area S increases, even when drawing an object from a macro viewpoint, an increase in calculation time can be avoided. While suppressing it, it is possible to express a feeling of brightness closer to the actual appearance.

The CG display unit 14 displays, as CG, paint colors (display colors) calculated for all pixels in the image to be drawn. The CG display section 14 is an example of an "output section".

Here, an operation example of processing for expressing the sense of brightness by the display device 1 will be described with reference to FIG. 8 . FIG. 8 is a flow chart showing the flow of processing performed by the display device 1 of this embodiment. The flow of processing for calculating the brightness of paint in a certain pixel as the display color of that pixel will be described below.

Step S1:
From the object shape information 120, the display device 1 acquires the position coordinates of the polygon and the normal line _n0 of the polygon as the polygon information of the object corresponding to the drawing pixel.

Step S2:
The display device 1 acquires the light source information for illuminating the object and the position information of the camera from the light source information camera information 123 .

Step S3:
From the painting information 121, the display device 1 obtains the predetermined area ΔS, the number N of the glittering materials 21 included in the predetermined area ΔS, and the normal lines under the surfaces of the glittering materials 21 as the information of the painting 20 corresponding to the drawing pixel. Get the variance ^s2 .

Step S4:
From the glitter material information 122, the display device 1 acquires the specular reflection coefficient k _s and the surface roughness σ ² of one glitter material as information on the glitter material 21 contained in the painting 20 corresponding to the drawing pixel. The display device 1 initializes the variable m to 0 (zero).

Step S5:
The display device 1 determines whether or not the variable m is greater than the number N. The number N is the number of glittering materials 21 included in the predetermined area ΔS, and is information stored in the coating information 121 . When the variable m is smaller than the number N, the display device 1 proceeds to step S6. That is, the display device 1 repeats the following steps S6 to S9 by the number N.

Step S6:
The display device 1 uses the dispersion information of the normal under the surface of the glitter material 21 acquired as the coating information 121 to calculate the normal under the surface of the glitter material 21 determined by the Gaussian distribution function.

Step S7:
The display device 1 draws from the normal under the surface of each glitter material 21 calculated in step S6, the light source and camera direction obtained from the light source information camera information 123, the glitter material information 122, and the drawing area S in the drawing pixel. Calculate the reflectance (specular reflection coefficient) by one glitter material drawn in a pixel.

In this case, the display device 1 calculates the number of glittering materials 21 included in the drawing area S by using the ratio of the drawing area S to the preset predetermined area ΔS. The reflectivity of the luster material is calculated approximately when the number is considered to be the same as the number, and the reflectance of the luster material is calculated using the approximately calculated reflection properties.

Step S8:
The display device 1 calculates the intensity of light incident on the glitter material in the drawing pixel.

Step S9:
Based on the specular reflection coefficient obtained in step S7 and the incident light intensity calculated in step S8, the display device 1 calculates the radiance I _s emitted from one glitter material in the drawing pixel as reflected light on the mirror surface of the glitter material. Calculate as a component.

Step S10:
The display device 1 increments the variable m and returns to the process shown in step S5. If the variable m is greater than the number N in step S5, the display device 1 proceeds to step S11.

Step S11:
The display device 1 sets the value obtained by adding the reflected light component (radiance I _s ) of each of the N glittering materials calculated each time steps S6 to S10 are repeated as the display color of the drawing pixel.

In the flowchart described above, the case where the respective radiances I _s are added after calculating the radiances I _s for N pieces has been exemplified and explained, but the present invention is not limited to this. The display color may be calculated by performing the process of adding the calculated radiance I _s N times each time the radiance I _s is calculated.

As described above, the display device 1 of the embodiment includes the acquisition unit 130, the subsurface normal calculation unit 131, the reflectance calculation unit 132, the incident light calculation unit 133, the specular reflection light calculation unit 134, A brightness addition unit 135 and a CG display unit 14 are provided. The acquisition unit 130 acquires object shape information 120 , painting information 121 , glitter material information 122 , and light source information camera information 123 . The subsurface normal calculation unit 131 uses the subsurface normal distribution degree of the painting information 121 and the object shape information 120 to calculate the subsurface normal of the glitter 21 included in the predetermined area ΔS. The reflectance calculator 132 calculates the reflectance of the glitter material 21 using the glitter material information 122 and the subsurface normal calculated by the subsurface normal calculator 131 . Reflectance is variable with light source and viewing direction. The reflectance calculator 132 calculates the reflectance of the glitter material 21 according to the distance d. The distance d is the viewpoint distance from the viewpoint position of the camera to the object. The incident light calculator 133 uses the light source information to calculate the incident light for the drawing pixels. The specular reflected light calculation unit 134 uses the reflectance calculated by the reflectance calculation unit 132, the incident light calculated by the incident light calculation unit 133, and the camera information to calculate the reflected light of the glitter material 21 to be drawn on the drawing pixel. Calculate the ingredients. The brightness addition unit 135 adds the reflected light components calculated by the specular reflection calculation unit 134 by the number of the brightness materials included in the drawing pixel to calculate the display color of the drawing pixel. The CG display unit 14 outputs (displays) the display color for each pixel calculated by the brightness adding unit 135 . Thus, in the display device 1 of the embodiment, the reflectance of the glitter material 21 can be calculated according to the viewpoint distance, and the reflectance can be calculated so as to express the object with an appropriate resolution according to the viewpoint distance. becomes possible. Therefore, even from a macro viewpoint, it is possible to efficiently express the feeling of brilliance with a small amount of calculation.

In addition, in the display device 1 of the embodiment, the reflectance calculation unit 132 is configured so that the number of glittering materials 21 included in the drawing area from the macro viewpoint is the same as the number of glittering materials 21 included in the drawing area from the microscopic viewpoint. In addition, it is assumed that an integrated glittering material obtained by integrating a plurality of glittering materials 21 is included in the drawing area in the macro viewpoint. The reflectance calculator 132 calculates the reflected light component of the integrated glitter material based on the reflection characteristics of the glitter material 21 and the ratio of the drawing area in the macro viewpoint and the drawing area in the micro viewpoint. Accordingly, in the display device 1 of the embodiment, the display color can be calculated by the calculation equivalent to that for the micro viewpoint even from the macro viewpoint. Moreover, since the reflected light component in the integrated glittering material can be calculated based on the reflection characteristics and the area ratio (S/ΔS) of the individual glittering materials 21 before integration, the reflection characteristics at the macro viewpoint can be adjusted to the viewpoint distance. It is possible to calculate so as to have the corresponding characteristics. Therefore, even from a macro viewpoint, it is possible to efficiently express the feeling of brightness with a small amount of calculation.

In addition, in the display device 1 of the embodiment, the reflectance calculator 132 controls the spread of the radiance of the light reflected by the glitter material 21 according to the line-of-sight angle. Thereby, the display device 1 of the embodiment can calculate the reflectance according to the drawing area S. FIG. Therefore, the same effects as those described above can be obtained.

In addition, in the display device ¹ of the embodiment, the reflectance calculation unit 132 changes the surface roughness σ2 of the glitter material 21 in the glitter material information 122 according to the drawing area S, so that the reflected light of the glitter material 21 is controls the spread of radiance as a function of line-of-sight angle. Accordingly, in the display device 1 of the embodiment, the reflectance can be calculated by calculating the surface roughness σ ² according to the drawing area S. Therefore, the same effects as those described above can be obtained.

In addition, in the display device 1 of the embodiment, the reflectance calculator 132 sets the number of glittering materials 21 included in the drawing area S to be the same as the number of glittering materials 21 included in the predetermined area ΔS. Thus, in the display device 1 of the embodiment, regardless of the drawing area S, the display color can be calculated with the same amount of calculation as when drawing an object with a predetermined area ΔS.

In addition, in the display device 1 of the embodiment, the reflectance calculation unit 132 makes the number of the glittering materials 21 included in the drawing area S equal to the number of the glittering materials 21 included in the predetermined area ΔS. Furthermore, it is assumed that the drawing area S includes an integrated glittering material obtained by integrating a plurality of glittering materials 21 . ^The reflectance calculator 132 calculates the integrated brightness so that the ratio of the surface roughness ^σ′2 of the integrated brightness material to the surface roughness σ2 of the brightness material 21 is the same as the ratio of the drawing area S to the predetermined area ΔS. Determine the surface roughness σ' ² of the material. Accordingly, in the display device 1 of the embodiment, it is possible to determine an appropriate surface roughness σ′ ² of the integrated glitter material according to the drawing area S.

In the above-described embodiment, when expressing the feeling of brightness in one pixel expressing painting, the reflected light is calculated using the ratio of the drawing area S of the pixel and the preset predetermined area ΔS. As a result, it is possible to express a sense of brilliance according to the viewpoint distance. In particular, in the present embodiment, it is possible to express the feeling of brightness at a high speed in the same manner as in the micro-viewpoint without the need to calculate reflected light from a huge number of glittering materials from the macro-viewpoint.

Further, in the above-described embodiments, the description has focused on the representation of the feeling of brilliance. However, of course, in painting, specular reflection occurs on the surface of the uppermost clear coat layer and diffuse reflection occurs on the lower pigment layer. It is conceivable that the reflected light from each of these layers may be separately calculated and added together in the CG display unit 14 to express a more complicated paint color.

Further, in the above-described embodiment, the surface roughness σ' ² and the specular reflection coefficient ks' are calculated using the ratio of the predetermined area ΔS and the drawing area S. In addition, it is conceivable to change or correct the above parameters (surface roughness σ′ ² and specular reflection coefficient ks′) based on the relationship of viewpoint distance to a certain resolution.

Further, in the above-described embodiment, parameters such as specular reflection coefficients ks, ks', surface roughness σ ² , σ' ² may be set for each color of RGB. Thereby, the color of the luster material 21 can be expressed.

In the above-described embodiment, after the radiance I _s (specular reflection radiance) of each glittering material 21 is calculated by the specular reflection calculation unit 134, the radiance I _s is added by the glitter adding unit 135. are being implemented. However, the reflectance of each glitter material 21 calculated by the reflectance calculator 132 may be added in advance, and then the specular reflected light calculator 134 may calculate the specular reflected light in the direction of the camera.

Further, in the above-described embodiment, the case where the reflection model used when estimating the reflection characteristics is the Ward model has been exemplified and explained. However, it is not limited to this. Any model other than the Ward model may be used to estimate the reflection characteristics. For example, a model suitable for metallic reflection, such as Cook-Torrance, may be employed to express the luster of aluminum flakes.

All or part of the display device 1 in the above-described embodiments may be realized by a computer. In that case, a program for realizing this function may be recorded in a computer-readable recording medium, and the program recorded in this recording medium may be read into a computer system and executed. It should be noted that the "computer system" referred to here includes hardware such as an OS and peripheral devices. The term "computer-readable recording medium" refers to portable media such as flexible discs, magneto-optical discs, ROMs and CD-ROMs, and storage devices such as hard discs incorporated in computer systems. Furthermore, "computer-readable recording medium" means a medium that dynamically retains a program for a short period of time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. It may also include something that holds the program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in that case. Further, the program may be for realizing a part of the functions described above, or may be capable of realizing the functions described above in combination with a program already recorded in the computer system. It may be implemented using a programmable logic device such as FPGA.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design and the like are included within the scope of the gist of the present invention.

DESCRIPTION OF SYMBOLS 1... Display apparatus (calculation apparatus), 11... Communication part, 12... Storage part, 13... Control part, 120... Object shape information, 121... Paint information, 122... Luster material information, 130... Acquisition part, 131... Under surface Normal calculation unit 132 Reflectance calculation unit 133 Incident light calculation unit 134 Specular reflection calculation unit 135 Brilliance addition unit 14 CG display unit

Claims (9)

A computing device for calculating the display color of an image that expresses the feeling of glitter in an object containing a glitter material by computer graphics,
Object shape information indicating the shape of the object, light source information indicating a light source for illuminating the object, camera information regarding a camera for virtually imaging the object, the number of the glittering materials contained in a predetermined area, and the glittering materials, respectively. an acquisition unit that acquires coating information indicating the degree of distribution of normals under the surface of and luster material information indicating the reflection characteristics of the luster material;
a subsurface normal calculation unit that calculates the subsurface normal of the luster material included in the predetermined area using the distribution degree of the subsurface normal and the object shape information;
Using the glitter material information and the subsurface normal calculated by the subsurface normal calculation unit, the reflectance of the glitter material with the light source and line of sight as variables is calculated from the viewpoint position of the camera to the object. a reflectance calculation unit that calculates according to the viewpoint distance;
an incident light calculation unit that calculates incident light for a drawing pixel to be drawn using the light source information;
specular reflection for calculating the reflected light component of the glittering material to be drawn in the drawing pixel using the reflectance calculated by the reflectance calculator, the incident light calculated by the incident light calculator, and the camera information; an optical calculation unit;
a brightness addition unit that calculates the display color of the drawing pixel by adding the reflected light components calculated by the specular reflection calculation unit by the number of the glitter materials included in the drawing pixel;
an output unit that outputs the display color for each pixel calculated by the brightness addition unit;
A computing device comprising The reflectance calculation unit determines that the number of the glittering materials included in the drawing area of the object drawn in the drawing pixel at the macro viewpoint with the large viewpoint distance is included in the drawing area at the micro viewpoint with the small viewpoint distance. Assume that an integrated glittering material obtained by integrating a plurality of glittering materials is included in the drawing area in the macro viewpoint so that the number of the glittering materials is the same as the number of the glittering materials, and the reflection characteristics of the glittering material and the drawing in the macro viewpoint calculating the reflectance in the integrated glitter based on the ratio of the area to the drawing area in the micro perspective;
2. The computing device of claim 1. The glitter material information is information indicating the specular reflection coefficient of the glitter material in the specular reflection model and the surface roughness of the glitter material.
3. A computing device according to claim 1 or claim 2. The subsurface normal calculation unit acquires, as coating information, information indicating dispersion according to a normal distribution as the degree of variation of the subsurface normal of the glitter material, and uses the dispersion to determine the normal line of the glitter material. to calculate
The normal distribution is a distribution that has a variation represented by the variance centered on the surface normal of the object to be drawn on the drawing pixels, and the zenith angle with respect to the surface normal is 0 on average.
4. A computing device according to any one of claims 1 to 3. The reflectance calculation unit controls the spread of radiance according to the line-of-sight angle in the reflected light of the glitter material according to the drawing area of the object drawn in the drawing pixels.
5. A computing device according to any one of claims 1 to 4. The reflectance calculation unit changes the surface roughness of the glitter material in the glitter material information according to the drawing area of the object to be drawn in the drawing pixels, thereby changing the line-of-sight angle of the reflected light of the glitter material. controls the spread of radiance according to
A computing device according to any one of claims 1 to 5. The reflectance calculation unit calculates a number of the glitter materials so that the number of the glitter materials included in the drawing area of the object drawn in the drawing pixels is the same as the number of the glitter materials included in a predetermined area. is included in the drawing area, and the ratio of the surface roughness of the integrated glitter material to the surface roughness of the glitter material is the same as the ratio of the drawing area to the predetermined area Determining the surface roughness of the integrated glitter material so that the ratio is
7. A computing device according to any one of claims 1-6. A calculation method performed by a computer device for calculating the display color of an image that expresses the feeling of glitter in an object containing a glitter material by computer graphics,
An acquisition unit obtains object shape information indicating the shape of the object, light source information indicating a light source that illuminates the object, camera information regarding a camera that virtually captures the object, the number of the glittering materials included in a predetermined area, and the Acquiring painting information indicating the degree of distribution of normals under the surface of each of the glittering materials, and glittering material information indicating the reflection characteristics of the glittering materials,
a subsurface normal calculation unit, using the distribution degree of the subsurface normal and the object shape information, calculates the subsurface normal of the glitter material included in the predetermined area;
A reflectance calculation unit uses the glitter material information and the subsurface normal calculated by the subsurface normal calculation unit to calculate the reflectance of the glitter material with the light source and line of sight as variables from the viewpoint of the camera. According to the viewpoint distance from the position to said object, calculate
an incident light calculation unit, using the light source information, calculates incident light for a drawing pixel to be drawn;
A specular reflected light calculation unit uses the reflectance calculated by the reflectance calculation unit, the incident light calculated by the incident light calculation unit, and the camera information to calculate the reflection of the glitter material to be drawn on the drawing pixels. Calculate the light component,
a glitter addition unit adds the reflected light components calculated by the specular reflection light calculation unit by the number of the glitter materials included in the drawing pixel to calculate the display color of the drawing pixel;
An output unit outputs the display color for each pixel calculated by the brightness adding unit;
Method of calculation. A computer device that calculates the display color of an image that expresses the feeling of glitter in an object containing a glitter material by computer graphics,
Object shape information indicating the shape of the object, light source information indicating a light source for illuminating the object, camera information regarding a camera for virtually imaging the object, the number of the glittering materials contained in a predetermined area, and the glittering materials, respectively. Acquisition step of acquiring coating information indicating the degree of distribution of normals under the surface of and glitter material information indicating the reflection characteristics of the glitter material,
a subsurface normal calculation step of calculating the subsurface normal of the glittering material included in the predetermined area using the distribution degree of the subsurface normal and the object shape information;
Using the glitter material information and the subsurface normal calculated by the subsurface normal calculation step, the reflectance of the glitter material with the light source and line of sight as variables is calculated from the viewpoint position of the camera to the object. a reflectance calculation step of calculating according to the viewpoint distance;
an incident light calculation step of calculating incident light for a drawing pixel to be drawn using the light source information;
Specular reflection for calculating the reflected light component of the glittering material to be drawn on the drawing pixels, using the reflectance calculated by the reflectance calculation step, the incident light calculated by the incident light calculation step, and the camera information. optical calculation process,
a brightness addition step of calculating the display color of the drawing pixel by adding the reflected light components calculated in the specular reflected light calculation step by the number of the glittering materials included in the drawing pixel;
an output step of outputting the display color for each pixel calculated by the brightness adding step;
program to run.

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