JPH1010045A - Method of determining optical property of metallic paint film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely determine the color at an optional light receiving angle within a wide range by calculating a regression expression and a regression coefficient by measured spectral reflectances at specified five angles, and determining the spectral reflectance at a desired angle. SOLUTION: The light receiving angle to a metallic paint film 1 is divided to 10-20 deg., 20-30 deg., 30-50 deg., 50-80 deg. and 80-110 deg.. The spectral reflectance at an optional angle of each section is measured by a portable spectrometer. A computer 3 determines three regression expressions and a regression coefficient within a prescribed light receiving angle range from the five spectral reflectances, and calculates a calculated reflectance at an interval of 1 deg. between receiving angles of 10 deg. to 110 deg.. After conversion into three stimulus values XYZ from the spectral reflectance, the emitting intensities of phosphors RGB of a monitor 5 are calculated from the characteristic table of a graphic monitor to display the table. Thus, the colorimetrically precise computer graphics of the metallic paint color can be inexpensively performed in a short time with a small-sized device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for determining the optical properties of a metallic coating and to a computer graphic apparatus.

[0002]

2. Description of the Related Art In order to enhance the design effect, a metallic paint is prepared by mixing a chromatic pigment and a scaly brilliant pigment (aluminum flake, pearl flake, etc.) or fine particle titanium oxide utilizing Rayleigh scattering in a binder. Is commonly used. The biggest feature of the color development is, depending on the viewing angle,
Brightness, saturation, and hue change to give various textures such as a metallic feeling and a pearly feeling. For color material manufacturers and manufacturers that manufacture and sell these metallic paint colors,
In the paint color design design using graphics, the color that changes color depending on the viewing angle is quantitatively measured,
Represented on product management and computer graphics
It is important to present to the audience.

However, it is difficult to measure such a paint color whose color changes depending on the angle. As a device for measuring at an arbitrary light receiving angle, a device generally called a goniospectrophotometer (for example, Murakami Color Research Laboratory Co., Ltd.) GCMS-4)
However, these devices are large and expensive, take a considerable amount of time to measure, and have a large amount of measured data and a large capacity for storing data. For this reason, computer graphics devices that are colorimetrically correct for metallic paint colors have not yet become widely used.

[0004] In order to improve such disadvantages of the colorimetric device, a device for measuring at a fixed light receiving angle, a so-called portable spectrophotometer, has been developed. Since this device is portable, it is small and portable, and has a fixed light receiving angle, so that the measurement time is extremely short, and the amount of measurement data is small.

However, this device is limited to a portable type, so that the measurable angle is limited to 3 to 5 angles. In this case, a highlight of a metallic paint color (a place where a person feels bright and dazzling at an angle close to regular reflection light) is used. Therefore, it is possible to continuously measure the color in a wide range of angles from a light receiving angle of, for example, 10 degrees to a shade (a light receiving angle of, for example, 110 degrees at a place far from the specularly reflected light, for example, a light receiving angle of 110 degrees). Did not.

Here, it is important to use the spectral reflectance as data used for color prediction as follows. An equation for predicting a wide range of colors with colorimetric data obtained from multiple angles has already been proposed in U.S. Pat. No. 4,479,718. However, this U.S. patent actually uses data obtained from three angles, and predicts from L * by a quadratic expression of angle, so that it is possible to predict only light and dark L *, and it also requires 45 degrees. At the above angle, there is a disadvantage that the accuracy of the regression equation is significantly inferior. In recent metallic paint colors, a bicolor paint color in which the color (mainly hue) changes depending on the angle has been required, and various glittering materials have been developed. Such a change in hue could not be calculated at all in the above-mentioned U.S. Patent.

Accordingly, an object of the present invention is to provide a method capable of accurately determining a color at an arbitrary light receiving angle over a wide range from a highlight to a shade from five light receiving angles obtained from a portable spectrophotometer. To provide.

Another object of the present invention is to obtain the same results as those measured with a large-size variable-angle spectrophotometer capable of measuring at an arbitrary light receiving angle without deteriorating the advantages of the portable spectrophotometer.

It is another object of the present invention to provide a computer graphics device which produces a colorimetrically correct metallic paint color.

It is another object of the present invention to provide a computer graphic device for determining the spectral reflectance of a metallized coating film at a desired angle, the computer graphic device requiring a very small storage capacity. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring to FIGS.
The property of the spectral reflectance of the metallic coating film will be described.

In general, the coating structure of the metallic coating color and the gloss distribution due to the change in angle are as shown in FIG. In a color base containing a chromatic pigment or a dye, scaly glittering materials (flakes of aluminum, mica, etc.) are arranged substantially in parallel.
The structure of the metallic coating film may be a so-called color clear coating color in which a color clear is applied on a metallic base containing no chromatic organic pigment.

FIG. 2 shows a typical example of the spectral reflectance of such a coating film structure. FIG. 2 shows the results obtained by measuring the incident angle at 45 degrees and the light receiving angle at an angle of 10 degrees to 120 degrees from the specularly reflected light in increments of 1 degree using a variable angle spectrophotometer GCMS-4 manufactured by Murakami Color Research Laboratory. It can be seen that at the spectral reflectance level, the light-receiving angle increases smoothly and decreases.

On the other hand, there are two methods for measuring the color: a method of obtaining a spectral reflectance for each change angle using a goniospectrophotometer, and a method of obtaining tristimulus XYZ using a gonio-colorimeter. The spectral reflectance is purely the spectrum of the object, and the attenuation of the reflectance due to the change in angle varies with each wavelength, but simply decreases. However, the tristimulus value XYZ is a value obtained by multiplying the human eye's visual luminous efficiency by the reflectance, and the way of change differs depending on the paint color because the visual luminosity is multiplied.
It is difficult to formulate the optical properties of metallic paint colors. The same applies to the color difference equation Lab *. Also, the spectral reflectance is information on a substance, and can be used as original data for a blending calculation by CCM (Computer Color Matching). Once the spectral reflectance is determined, the tristimulus value XY is calculated from the spectral reflectance.
Z, and from the tristimulus values XYZ to the color difference equation Lab *, as is well known, JIS Z8701, Z872.
9 can be easily calculated. Therefore, it is important that the color measurement method is not a method of obtaining the tristimulus values XYZ but a method of obtaining the spectral reflectance.

For example, a color in a wide angle range from a highlight at an angle position of 10 degrees to specular reflection to a shade at an angle position of 110 degrees to specular reflection is determined from a smaller measured reflectance. As a result of detailed study of the deflection characteristics at 45 degree incident light of metallic paint color,
The following four points became clear.

1) In a specularly reflected light region, which is a region with a very small deflection angle (for example, 10 degrees or less), the reflectance is very high, and it is almost flat and close to white light. Rather, it has a strong luster.

2) Small deflection angle (for example, 10 to 30)
In the highlight area, which is a degree area, the reflectance changes sharply and linearly.

3) Intermediate deflection (for example, 30 to 80 degrees)
In the face color area, which is the area (1), the reflectance smoothly changes in a curved manner.

4) Large deflection angle (for example, 80 to 110)
In the shade area, which is a degree area, the reflectance gradually and linearly decreases.

From the above research results, for example, from the highlight to the shade, that is, in order to determine the color at a light receiving angle of 10 to 110 degrees, the following five angles (X1,
X2, X3, X4, X5) were selected. X1 is 10-2
Any angle between 0 degrees, X2 any angle between 20-30 degrees, X3 any one angle between 30-50 degrees,
X4 is an arbitrary angle between 50 to 80 degrees, and X5 is 80 to 80 degrees.
Any one angle between 100 degrees. The regression coefficient of the regression equation was determined by the least squares method using the reflectance measured at these five angles as the objective function (R (X)) and the light receiving angle as the dependent function (X). According to the range of the light receiving angle, for example, it has been found that the actually measured value and the calculated value are extremely coincident by adopting, for example, the following three function types. In this equation, a1, a2, a3, b1, b2, b3,
c2 is a regression coefficient obtained by the least square method.

R (x) = exp (a ₁ x + b ₁ ) 10 ≦ x <30 (1) R (x) = exp (a ₂ x ² + b ₂ x + c ₂ ) 30 ≦ x <80 (2) R (x) ) = A ₃ x + b ₃ 80 ≦ x <110 (3) In this embodiment, as described above, in the highlight region, the reflectance changes sharply and linearly. In a region, the reflectance changes smoothly in a curved manner, and the above formula (2) is used. In a shaded region, the reflectance decreases gradually and linearly, so the above formula (3) is used.

The accuracy of the predicted value R '% using the equations (1) to (3) is as small as about 2 even at 10 degrees, which is an extrapolation angle, and almost equal to or less than 1 in a wide range from 15 degrees to 110 degrees. Fits in. Generally, if the color difference (NBS unit) is 1 or less in color merchandise transactions, it is considered that the colors are equal, and considering that this is used as a shipping standard, the estimation accuracy of the highlight (10 degrees) is 2 in color difference, and the target 1 It has been empirically known that the visual sensitivity is reduced at 10 degrees, which is slightly higher than 10 degrees but has a very high reflectivity. Therefore, in practice, a wide range from 10 degrees to 110 degrees is obtained by using the equations (1) to (3). The color can be determined with high accuracy.

Referring now to FIG. 3, a computer graphics device according to a preferred embodiment of the present invention will be described.
The computer graphic apparatus measures the metallic coating film 1 with a portable spectrophotometer 2 and takes the obtained five-angle reflectivity into a computer 3, and calculates the above-mentioned formula (5) from the five-angle reflectivity. 1) to (3) and the regression coefficient are obtained, and the calculated reflectance is determined at intervals of 1 degree from 10 degrees to 110 degrees (may be 1 degree or less depending on the resolution of the image to be created), and from the reflectance, Converted into tristimulus values XYZ,
Based on the tristimulus values XYZ, the light emission intensity of the phosphor RGB of the monitor 4 is calculated from the characteristic table of the graphic monitor, and the color is displayed. This computer / graphic device can carry out colorimetrically correct computer graphics in a short time and inexpensively with a small device.

Further, for example, when a computer graphics device is used to create an image of an automobile without deteriorating the texture of metallized colors, which is the most common in automobiles, the conventional method is as follows.
The input data was obtained by continuously measuring 16 spectral reflectances (in the case where the wavelength range from 400 nm to 700 nm was measured at 20 nm) over a wide range from 0 to 110 degrees at a measurement angle of 1 degree or less. . In this case, if the data is stored in real number 4 bytes assuming that the measurement is performed in steps of once, a storage capacity of [(110-10) +1] * 4 * 16 = 6464 bytes is required. On the other hand, according to the present invention, it is well known inside a computer that the reflectance of 5 angles is stored with a very small storage capacity of 5 * 4 * 16 = 320 bytes (only 5%). By using the least-squares method program, the regression equation and the regression coefficient are calculated, and the reflectance at an arbitrary angle can be calculated. Further, if the accuracy of computer graphics is to be determined at intervals of 0.5 degrees in order to improve the accuracy of the computer graphics, the storage capacity required in the conventional method increases in proportion to the number of measurement angles, but the reflectance of only 5 angles in the present method. Is enough. This is because the reflectance at an arbitrary angle can be calculated by the equations (1) to (3).

A goniospectrophotometer for continuously measuring with a gonio is extremely expensive. If the number of measurement angles increases, the measurement time becomes enormous, and an image of a metallic paint color is created based on this data. Therefore, a great deal of effort was required to create one image. However, according to the present method, data of only five angles is sufficient, so that a small and inexpensive measuring device can be used, and the measuring time can be very short. It is possible to obtain the reflectance in a wide range of angles that is sufficiently practical. By using this formula, it is possible to quickly and easily create a computer graphic having a colorimetrically correct metallic paint color.

[0026]

EXAMPLES The accuracy of the above-mentioned formulas (1) to (3) of the gold metallic containing the metallic coating color (aluminum flake, yellow organic pigment, fine particle titanium) was confirmed at a wavelength of 660 nm. The angles used for verification were X1 = 15 and X2 =
25, X3 = 45, X4 = 75, X5 = 110 were used. To create the regression coefficients of the above equations (1) to (3), the equation (2) is obtained from two data of 15 and 25 degrees in the equation (1).
From the data at 25, 45, and 75 degrees, 7
Calculated from 2 data at 5,110 degrees. As a result, although the error was large when the highlight was 10 degrees or less, the measured value and the calculated value were very good in other cases.

Next, in order to examine whether or not the above formulas (1) to (3) can be applied to various metallic paint colors, the hue, lightness, and color including metallic, pearl, plate-like iron oxide and microtitanium are examined. The 72 paint colors with different degrees were applied by GCMS-4 at an incident angle of 45 degrees and a light receiving angle of 5 degrees between 10 degrees and 110 degrees.
Spectral reflectance was measured at every step, and sampling was performed at intervals of 20 nm in a wavelength range of 400 to 70 nm, and 16 reflectances were obtained. The angles used for verification were each X1 = 1
5, X2 = 25, X3 = 45, X4 = 75, X5 = 11
0 was used. To create the regression coefficient of Equation 3, 1 is used in Equation (1).
From the two data of 5, 25 degrees, in equation (2), 25, 4
In equation (3), calculation was performed from two data at 75 and 110 degrees from the data at 5, 75 degrees. The result is shown in FIG. 4 as an average color difference of 72 colors. As shown in FIG. 4, the color difference near the highlight was a little as large as about 2, but otherwise the color difference was within about 1.

[Brief description of the drawings]

FIG. 1 is a diagram showing a coating structure of a metallic coating color and a gloss distribution due to a change in angle.

FIG. 2 is a graph showing a reflectance value of 660 nm measured from 10 degrees to 120 degrees of a gold metallic paint color and formulas (1) to
The figure which shows the value determined according to (3).

FIG. 3 is a diagram showing a computer graphics device according to an embodiment of the present invention.

FIG. 4 is a diagram showing a color difference between an actually measured value of 72 paint colors and a value determined according to the present invention.

[Explanation of symbols]

 1 Metallic coating 2 Spectrophotometer 3 Computer 4 Monitor

Claims (6)

[Claims] 1. A method for determining the optical properties of a metallic coating film containing a scaly glittering material or fine-particle titanium oxide causing Rayleigh scattering and having a color that changes depending on the angle, comprising a step of measuring the metallic coating film at five angles. Determining a spectral reflectance at a desired angle of the metallic coating based on the reflectance and a regression equation and a regression coefficient calculated based on the spectral reflectance measured under the conditions of the above five angles. A method for determining optical properties. 2. A light receiving angle of 10 at an incident angle of 45 degrees.
Five angles X1, X2, selected between 110 degrees
2. The method according to claim 1, wherein the regression equation and the regression coefficient are calculated using the measured reflectances of X3, X4 and X5. 3. The X1 is an arbitrary angle between 10 and 20 degrees, the X2 is an arbitrary angle between 20 and 30 degrees, and the X3 is an angle between 30 and 50 degrees. 3. The metallic coating of claim 2 wherein X4 is any angle between 50 and 80 degrees and X5 is any angle between 80 and 110 degrees. A method for determining the optical properties of a film. 4. The regression equation includes a first regression equation corresponding to a change in reflectance in a highlight area, a second regression equation corresponding to a change in reflectance in a face color area, and a reflection equation in a shade area. Third responding to rate changes
3. The method for determining the optical properties of a metallic coating film according to claim 2, which comprises the following regression equation. 5. A spectrophotometer for measuring a spectral reflectance of a metallic coating film at five angles, and a computer for determining a spectral reflectance at a desired angle from the measured spectral reflectances at the five angles. And wherein the computer has 5 measured by the spectrophotometer.
Means for calculating a regression equation and a regression coefficient from the spectral reflectance under the angle condition, and a desired angle of a metallic coating film from the five angles of spectral reflectance measured by the spectrophotometer, the regression equation and the regression coefficient. A computer graphics device comprising means for determining a spectral reflectance. 6. A means for storing the spectral reflectance under five-angle conditions measured by a spectrophotometer, and calculating a regression equation and a regression coefficient from the spectral reflectance under five-angle conditions read from the storing means. Means for determining the spectral reflectance at a desired angle of the metallic coating from the spectral reflectance under the five-angle condition read from the storing means, the regression equation, and the regression coefficient. A computer graphics device characterized by the following: