JPH05324850A - Rendering device - Google Patents

Abstract

PURPOSE:To reproduce the surface color of a body into a color matching a visual feeling regardless of the shape of the body and the color of the surface. CONSTITUTION:The energy of light which is found by a light distribution arithmetic part 24 according to environment light and the shape of the body stored in storage parts 15 and 18 and projected to the body surface, is calculated from a fine area spectral reflection factor and a three-dimensional spectral three-dimensional angle reflection factor stored in storage parts 12 and 14 to find the emission luminance of spectral light traveling to a view point for constituent pixels of a display screen, thereby finding three XYZ color specification stimulation values. This processing is performed for all the constituent pixels of the display screen to reproduce light and shade depending upon an angle and colors depending upon the wavelength of a fine area, thereby displaying an image of the body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rendering device, and more particularly to a rendering device which enables a three-dimensionally realistic reproduction display of an object by image processing such as computer graphics.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
For an object whose surface has uniform optical properties, 2
There is a method to reproduce and display an object three-dimensionally and realistically by performing coloring calculation based on the ray tracing method using the three-dimensional spectral solid angle reflectance (A. Takagi et al, Computer Gr.
aphics, Vol 24, No. 4, 1990).

This method is based on the spectral solid angle reflectance of the object surface, etc., as shown in the following equation (1).
(International Commission on Illumination) Obtain standard XYZ color system color values (tristimulus values) and convert them to the color values specific to the color system by the linear linear combination conversion shown in the following equation (2). , .Gamma. Correction is performed and RGB gradation is converted to display a reproduced image of the object.

[0004]

[Equation 1]

[0005]

[Equation 2]

However, Y _R , Y _G , Y _B : luminance value of RGB color system A: a _ij (i, j = 1, 2, 3) color matching conversion matrix a _ij : display device Eigenvalue (determined by measuring the brightness of the display screen).

According to this method, the luminous flux having the luminance L (λ, Θ) incident on the minute area on the surface of the object at an angle θ is reflected at the spectral solid angle reflectance R (λ, Φ) and the image display position. (That is, the luminous flux per minute solid angle toward the viewpoint)
Obtainable. By integrating this with respect to the solid angle, the luminance can be obtained when all the luminous fluxes incident from all the solid angles pass through one pixel of the screen forming the image. Based on this, the tristimulus values of the XYZ color system are converted.

However, the above method can be applied to an object having a uniform surface spectral reflectance, but since the spectral solid angle reflectance is a measured value in a wide range of the object, an object having a non-uniform spectral reflectance on the surface is used. For example, application to an object having a fine color pattern was impossible. Further, an object having a complicated reflection characteristic such as a woven fabric has a different spectral reflectance depending on the direction in which the object is viewed, and therefore cannot be applied to this object.

Further, in order to apply the above method to an object whose surface has a non-uniform spectral reflectance, the spectral solid angle reflectance of a minute area of the object is required over the entire surface. It is not possible to obtain the desired amount of measurement because there is no existing device to measure the spectral solid angle reflectance across. In addition, even if available, the measured value must be held over the entire surface of the object corresponding to the wavelength for a combination of three-dimensional angle conditions, which results in an enormous amount of data storage. System configuration is difficult.

By the way, as a method of displaying a fine color pattern on an object, a texture mapping method (JFBlin
n et al, Communication of the ACM, Vol.19, No.10,197
There is 6). By using this method, a fine pattern can be displayed by mapping a plane pattern onto the surface of the object.

However, this method is generally RG measured based on the three-color separation method by a color scanner or the like.
The B color system color value is mapped as pattern data, and it is effective for displaying a pattern on the surface of an object, but it is not possible to perform accurate uniform color reproduction display on the object surface. That is, since the colorimetric value for mapping is a value measured under a certain light source and is uniquely determined, the colorimetric value is changed according to the spectral energy change of the incident light, for example, the light source is changed. Can not do it. Also, since the RGB color system is a color system unique to the measurement system,
The conversion to another color system is complicated and the accuracy at the time of conversion becomes low. Furthermore, since the angle condition for measuring the colorimetric value is uniquely determined by depending on the measurement system of the measuring device such as a color scanner, it is impossible to obtain the colorimetric value under any angle condition.

In consideration of the above facts, an object of the present invention is to obtain a rendering device capable of reproducing the surface color of an object as a color that matches the visual sense, regardless of the shape and surface state of the object. is there.

[0013]

In order to achieve the above object, the present invention provides a spectral energy of a light source with which an object is irradiated,
Based on the calculated spectral radiant energy, the radiant energy calculating means for calculating the spectral radiant energy for each of the minute regions using the spectral reflectance in the minute area of the object and the spectral solid angle reflectance in the wide range of the object. Colorimetric value computing means for computing the colorimetric values of the colorimetric system, converting means for converting the colorimetric values into image data for image display, and display for displaying the image of the object based on the image data Means and are provided.

[0014]

When the object is viewed, the light reaching the viewpoint position from the surface of the object is related to the spectral energy of the light source illuminating the object and the surface reflectance of the surface of the object. That is, the light emitted from the light source reaches the viewpoint position as light of a color that has reached the surface of the object and is diffused or transmitted through the surface of the object. Therefore, in order to display the image of the object so as to match the visual state, the image data may be formed in consideration of the spectral energy of the light source illuminating the object and the surface reflectance of the object surface.

Therefore, the rendering apparatus of the present invention is provided with a radiant energy calculating means, which radiant energy calculating means has a spectral energy of a light source with which the object is irradiated, a spectral reflectance in a minute region of the object, and a wide range of the object. Spectral radiant energy is calculated for each minute region using the spectral solid angle reflectance. As the spectral solid angle reflectance, a value in a wide range of the object may be used, and a large value is not used. The colorimetric value calculation means calculates the colorimetric value of the colorimetric system based on the obtained spectral radiant energy, and the calculated colorimetric value is converted into image data for image display by the conversion means. The display means displays an image of the object based on this image data.

As described above, by synthesizing the relationship between the wavelength dependence of the minute region of the object and the angle dependence of the wide range, the light and darkness depending on the angle and the color depending on the wavelength of the minute region are reproduced for the minute region. It is possible to obtain the spectral radiant energy for, and to display an image based on the spectral radiant energy obtained for all minute areas of the object surface, so that the color and pattern faithful to the actual object surface can be obtained without using a large amount of data. The image of the object can be displayed with.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a configuration to which the rendering device of the present invention can be applied. In the present embodiment, the present invention is applied to a computer graphic in which an object is realistically displayed by coloring a color of an actual object on an image based on a surface model such as CAD and displaying it on a screen.

As shown in FIG. 1, the rendering apparatus 10 of this embodiment has a coloring calculation section 26. A data storage unit 12 that stores the spectral reflectance of a minute region and a data storage unit 14 that stores a wide range of three-dimensional spectral solid angle reflectance are connected to the coloring calculation unit 26. Although details will be described later, the data stored in the data storage unit 14 is used by the coloring calculation unit 26 after being standardized by the spectral solid angle reflectance of the reference angle condition stored in the data storage unit 22. Further, the coloring calculation unit 26 is connected to the light distribution calculation unit 24.

The light distribution calculating unit 24 is for calculating the spectral radiance of the ambient light incident on the minute area, and stores the ambient energy data storage unit 1 for storing the spectral energy of the light serving as the light source.
6, a shape data storage unit 18 that stores line drawing data such as CAD that describes the surface of an object, and a parameter storage unit 20 that stores a plurality of parameters for designating pixels and directions on the screen corresponding to the viewpoint and line of sight are connected. Has been done.

Therefore, the coloring calculation unit 26 displays the image from the small area on the object surface based on the spectral reflectance of the input minute area, the wide range of three-dimensional spectral solid angle reflectance, and the spectral radiance of ambient light. Then, the spectral radiance toward the pixels forming the XYZ colorimetric system is obtained and the tristimulus values are output.

Further, the coloring calculation section 26 has a color matching conversion section 28.
And the color matching conversion unit 28 is connected to the input XY
Data obtained by converting the Z color system color values, that is, the tristimulus values, into the RGB color system color values according to the coefficient data for color matching conversion stored in the conversion matrix storage unit 30 is displayed on the display unit 32. Output. The display unit 32 displays a color image according to the input RGB colorimetric value.

Next, XY in the coloring calculation unit 26
The output principle (coloring model) of tristimulus values in the Z color system will be described.

In order to reproduce and display the color pattern of the object surface as an image, that is, to match the color pattern of the object surface when visually observed with the color pattern of the object when the object is displayed as an image, the optical pattern on the object surface is used. A faithful grasp of nature is required. That is, the light for visually observing the object is light of brightness and color that is affected by the light emitted to the object being diffused or transmitted through the surface of the object. Therefore, the light reaching the viewpoint position when viewed from the object surface is related to the spectral energy of the light source illuminating the object and the surface reflectance of the object surface.

Therefore, in displaying an image of this object, the light reflected by the spectral energy of the light source with which the object is irradiated is determined by the spectral reflectance in a minute region of the object and the angular condition of the object for the color pattern of the object. The spectral radiant energy toward the viewpoint position corresponding to the screen pixel is obtained by weighting and specifying the change in brightness with the spectral solid angle reflectance in a wide range, and the tristimulus value of this energy is obtained. This can be expressed by the following expression (3).

[0025]

[Equation 3]

However, R _S (λ, Φo): Spectral reflectance of a minute area under the angle condition Φo Φo: Angle condition in which the incident angle, the reflection angle, and the azimuth angle are predetermined values. Angle (incident angle 45 °, reflection angle 0 °, azimuth angle 0 °, etc.) Further, Y _3D ^* is the angle-dependent normalized reflection ratio at the wavelength λ shown in the following formula (4). Represent

[0027]

[Equation 4]

However, R _3D (λ, Φ): Wide range of three-dimensional spectral solid angle reflectance Φ ^* : Reference angle condition For example, when the angle condition Φ is changed, the value of R _3D (λ, Φ) is medium An angle condition that indicates the reflectance of.

As described above, the light incident on the minute area of the object is reflected by the spectral reflectance R _s (λ, Φo) of this minute area, which is standardized by the wide range of three-dimensional spectral solid angle reflectance. The reflection rate Y _3D ^* (λ, Φ) gives a weight depending on the angle condition to adjust the brightness. As a result, the wavelength dependence of the minute region and the angle dependence of the wide range are combined, and the brightness depending on the angle and the color depending on the wavelength of the minute region can be reproduced. Therefore, by displaying the reproduced color of the minute area on all the object surfaces, it is possible to form an object display screen with colors and patterns that are faithful to the actual object surface.

The operation of this embodiment will be described below together with the rendering procedure. As shown in FIG. 4, first, in step 102, light distribution calculation is performed. This light distribution calculation is performed in the light distribution calculation unit 24 according to the viewpoint position (pixels on the screen) specified by the parameter storage unit 20 and the viewpoint direction from the viewpoint to the object in an environment in which light is incident on a minute area on the surface of the object. The spectral radiance of light is obtained.

In this embodiment, a three-dimensional ray tracing method is used for this light distribution calculation. In this ray tracing method, a ray reaching a minute area of an object from a light source is obtained by tracing the ray from the viewpoint toward the light source in the opposite direction of the light direction. When there are one or more other objects in addition to the target object in the optical path at the time of ray tracing, reflection or transmission processing is performed according to the optical properties of the other objects.

This ray tracing is performed by determining whether or not the ray and the object intersect at the time of tracing. In this example,
The shape data stored in the shape data storage unit 18 is used for this determination. The shape data may be described by a surface model of a polygon or a free-form surface, and the process of determining the presence / absence of intersection can be determined by the presence / absence of an intersection point obtained by a numerical operation of an algebraic polynomial. Further, in the processing of this ray tracing, it is also determined whether or not the ray at the time of tracing intersects the light source.

Therefore, by the intersection processing for obtaining the intersection by ray tracing, based on the spectral energy of the light source for irradiating the object stored in the ambient light data storage unit 16 or the like, a small solid angle is incident on a minute area on the surface of the object. The spectral radiance L of can be obtained. The ray tracing is performed not only between the object and another object or a light source, but also between the viewpoint and the object. Thereby, the incident angle with respect to the normal to the surface of the object can be obtained.

In the next step 104, as will be described in detail later, the spectral radiance directed from the minute area on the object surface to the position (viewpoint) corresponding to the pixels forming the screen is obtained. That is, in the coloring calculation unit 26, the 1
The spectral radiance I (λ, Φ) toward the pixel is obtained. At this time, since the reflection calculation is performed on the minute area on the surface of the object, the spectral reflectance of the minute area stored in the data storage unit 12 is associated with the position of the pattern surface that becomes the pattern of the minute area. In addition, the data storage unit 1 may be used depending on the angle condition between the incident light beam and the pixel.
The wide range three-dimensional spectral solid angle reflectance stored in 4 is used. Next, the obtained spectral radiance I (λ, Φ) is C
It is converted into the XYZ color system color value using the IE standard color matching function.

In the next step 106, the obtained XYZ
The colorimetric value (tristimulus value) is converted into the colorimetric value of the RGB colorimetric system. That is, the XYZ color specification values obtained by the coloring calculation unit 26 are converted by the RGB color matching conversion unit 28 into the conversion matrix storage unit 3.
It is converted into the RGB color system using the conversion matrix stored in 0. The converted colorimetric values are further corrected and converted into RGB gradation using the respective γ correction curves of RGB. This R
One pixel converted into the GB gradation is displayed on the display unit 32, that is, the screen (step 108).

By repeating the above procedure for all pixels on the screen of the display unit 32, image data for one screen is formed. Therefore, the display unit 32 on which the image based on the image data of this one screen is displayed has a realistic 3
A three-dimensional image is formed.

Next, with reference to FIGS. 2, 3 and 5, the coloring operation process of step 104 will be described in detail.

First, the spectral distribution 4 incident on the minute region 4
The light having 0 becomes light that emits the spectral radiance L ′ of the approximate spectral distribution 46 according to the reflectance distribution 42 of this minute region. Therefore, the spectral radiance L (λ, Θ) that is incident on the minute area on the object surface from the minute solid angle Δω obtained by the light distribution calculating section 24, and the spectral reflectance in the minute area stored in the data storage section 12 By synthesizing (for example, multiplying) R (λ, Φ) by the synthesizing operation processing 48,
Spectral radiance L '(λ, Θ) in the minute area is obtained (step 110).

Next, a wide range of three-dimensional spectral solid angle reflectance R of the object stored in the data storage unit 14
_3D (λ, Φ) is the three-dimensional spectral solid angle reflectance R _3D (λ, Φ) of the reference angle condition Φ ^* stored in the data storage unit 22.
The angle-dependent spectral reflectance ratio Y _3D ^* (λ, Φ) of the wavelength λ, which is standardized by the coefficient ρ that is ^* ), is obtained (step 11).
2). The spectral reflection ratio Y _3D ^* is obtained by combining the spectral characteristics 44 with the coefficient ρ by the combining calculation process 52.
Will have. The reflection ratio Y _3D ^* makes it possible to adjust the brightness of the object.

The spectral radiance L ″ (λ, Θ) toward the viewpoint is obtained using the spectral radiance L ′ and the spectral reflection ratio Y _3D ^* in these minute areas (step 114).
In this case, the spectral radiance L ″ has a spectral characteristic 56 obtained by synthesizing (for example, multiplying) the spectral radiance L ′ of the spectral distribution 46 and the reflection ratio Y _3D ^* of the spectral characteristic 54 by the synthesizing calculation process 50. become.

Therefore, the light incident on the minute area of the object surface from the minute solid angle Δω is reflected with the wavelength-dependent reflectance, and is further conditioned with the angle-dependent reflection ratio so as to satisfy the angle condition toward the viewpoint. , Has a spectral radiance L ″ toward the viewpoint.

Next, the total solid angle Ω desired by the minute area is the sum (Ω = Σω) of the minute solid angles Δωi (i = 1, 2, ..., N).
i), the above processing is performed for each minute solid angle Δωi to obtain the spectral radiance L ″ i for each minute solid angle Δωi, and the total radiance L ″ i of each spectral radiance L ″ i is calculated. The total sum is calculated to obtain the spectral radiance I (λ, Φ) of the light incident from the entire solid angle Ω, which is reflected by a minute area and travels toward the viewpoint (steps 116 and 118).

With respect to the obtained spectral radiance I, three color matching functions having spectral characteristics 66, 68 and 70 are combined and integrated by an integration calculation process 72 to obtain a tristimulus value XYZ of the XYZ color system. (Step 120), the coloring calculation process ends.

The spectral radiance I can also be obtained by performing reflection / transmission processing while tracing the optical path in the reverse direction as in the ray tracing method, and finally summing up in pixel units.

As described above, in the present embodiment, it is possible to change the color or pattern of a minute area by obtaining the light emitted from the object surface using the characteristics of the light source and the spectral reflectance of the object surface. Moreover, by using the three-dimensional spectral solid angle reflectance of the object, it is possible to form an image on the screen in which the brightness changes according to the three-dimensional angle condition. Therefore, even if you freely change the angle for viewing the object, that is, the viewpoint position and the type of light source that illuminates the object,
An image corresponding to the object can be formed on the screen.

In the above embodiment, the case where an object having a fine color pattern on the surface is rendered has been described, but as another embodiment, a case where a plain object is rendered will be described.

In the other examples, since the brightness change due to the angle condition is large for a plain object, it is emphasized, but since the change of the color pattern is small, the spectral reflectance is averaged. Is based on the fact that there is no great influence on the image formed on the display section.

That is, in the coloring model of the above equation (3), the spectral reflectance R _S (λ, Φo) of the minute area under the reference angle condition Φo and the three-dimensional spectral solid angle reflectance under the wavelength λ and the angle condition Φ. Swap the roles of and with R _3D (λ, Φ). Further, the reflectance ratio is calculated by taking the average value of the reflectance data in a predetermined area on the basic surface of the pattern data, and standardizing the reflectance with this value. This can be expressed by the following expression (5).

[0049]

[Equation 5]

However, Y _S ^* represents the reflectance ratio normalized by the average reflectance of a predetermined area as shown in the following equation (5).

[0051]

[Equation 6]

In this case, the light incident on the minute area of the object is standardized by the average reflectance of this minute area, and the brightness is reflected based on the angle condition of the wide range of three-dimensional spectral solid angle reflectance. This means that you can reproduce the light and darkness depending on the angle. Therefore, it is possible to display an image of an object having a slight change in brightness.

It should be noted that instead of giving the angle-dependent standardized reflection ratio described in the equation (4) of the above embodiment, the angle-dependent standardized luminance ratio can be changed. That is, in this case, the angle-dependent normalized reflection ratio Y _3D ^* (λ,
Φ) is given by changing to the angle-dependent normalized luminance ratio shown in the following formula (7). Therefore, this expression (7) can be given by a luminance ratio that incorporates the luminosity factor, while the above expression (4) gives a change in lightness and darkness with a standardized reflection ratio. It is possible to obtain a close value. However, since the spectral distribution of the standard light source is used to obtain the brightness, it does not directly reflect the incident light distribution at the time of calculation.

[0054]

[Equation 7]

However, C (λ): Spectral distribution of standard light source k ′: Normalization coefficient.

Further, the reflectance ratio Ys ^* (λ, Φo) standardized by the average reflectance shown in the formula (6) of the above embodiment is changed to the normalized luminance ratio shown in the following formula (9). You can also give it.

[0057]

[Equation 8]

The above equation (7) or equation (9) is
Since the spectral distribution C (λ) of the standard light source is known,
It can be calculated in advance.

As described above, the rendering apparatus of this embodiment can display a three-dimensional photorealistic object image with a small amount of data. Therefore, the design design in industrial design, the color and texture of the material, etc. It is suitable for evaluation and interior lighting design, and can be easily applied.

[0060]

As described above, according to the present invention, it is possible to change the color or pattern of a minute area based on the characteristics of the light irradiated on the object surface and the reflectance of the object surface, and Since it is possible to form on the screen an image in which the brightness changes according to the three-dimensional angle condition based on the three-dimensional spectral solid-state reflectance of the object, it is possible to reproduce and display the image of the object that matches the visual state. There is an effect that you can.

Further, since the amount of reflectance data used is small, there is no need to store a large amount of data or read it out in a long time, and a device configuration for reproducing and displaying an image of an object can be easily constructed. The effect is that you can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a rendering device according to an embodiment of the present invention.

FIG. 2 is an image diagram showing a process of obtaining a spectral radiance of light toward a viewpoint.

FIG. 3 is an image diagram showing a process of obtaining an XYZ color system color specification value from a spectral radiance of light traveling toward a viewpoint of all solid angles.

FIG. 4 is a flowchart showing a rendering procedure including coloring calculation processing in the present embodiment.

FIG. 5 is a flowchart showing a coloring calculation process of this embodiment.

[Explanation of symbols]

 10 Rendering Device 26 Coloring Operation Unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Suzuki, Nagakute-cho, Aichi-gun, Aichi, Nagatogi 1 1st side street, Toyota Central Research Institute Co., Ltd. (72) Inventor Keiko Watanabe Nagakute, Aichi-gun, Aichi Toyota Central Research Laboratory Co., Ltd. 1 at 41 Yokochi (72) Inventor Atsushi Takagi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Automobile Co., Ltd.

Claims (1)

[Claims] 1. Spectral radiant energy is obtained for each micro area using spectral energy of a light source with which an object is irradiated, spectral reflectance in a minute area of the object, and spectral solid angle reflectance in a wide range of the object. Radiant energy computing means, colorimetric value computing means for computing a colorimetric value of a colorimetric system based on the obtained spectral radiation energy, and conversion means for converting the colorimetric value into image data for displaying an image. A rendering device that displays an image of the object based on the image data.