Texture Interpolation

Abstract

Disclosed herein is a method for generating a digital representation of coatings on car parts. The method provides improved texture blending for the rendering of car paint sparkle. Further disclosed herein is a respective computer system.

Claims

1. A method for generating a digital representation of a car part coated with a paint comprising effect pigments, the method comprising: using a bi-directional texture function (BTF) of the paint to simulate the appearance of the paint on a 3D object using rendering software, wherein the BTF comprises a plurality of texture images representing the sparkling of the paint’s effect pigments for different viewing and illumination directions, and, wherein a smoothstep function $S_1\left(x\right)={\text{S}}_1\left({\text{x}}^{+}\left({\text{x}}^{\ast },{\text{t}}_{\text{n}},\text{w}\right)\right)={\text{S}}_1\left(\frac{{\text{x}}^{\ast }-{\text{t}}_{\text{n}}+\frac{\text{w}}{2}}{\text{w}}\right)$ in an interval with width w around a random transition point t .sub.n is used to interpolate pixel intensities at the local coordinate x* between the plurality of texture images.

2. The method of claim 1, wherein the transition point t.sub.n is randomly chosen in the interval [w/2, 1 - w/2] once for every pixel in the texture image.

3. The method of claim 1, wherein the smoothstep function takes the form $S_1\left(x\right)=\left\{\begin{array}{cc}0& x\le 0\\ 3x^2-2x^3& 0<x<1\\ 1& 1\le x\end{array}\right)$ $S_1\left(x,y\right)=S_1\left(x\right)\cdot S_1\left(y\right).$ .

4. The method of claim 3, wherein the interpolated pixel intensity is calculated according to $\begin{array}{l}I\left({\theta }_i^{+},{\theta }_h^{+},x\right)=S_1\left({\text{θ}}_i^{+}\right)S_1\left({\text{θ}}_h^{+}\right)I_{00}\left(x\right)+S_1\left({\text{θ}}_i^{+}\right)S_1\left(1-{\text{θ}}_h^{+}\right)I_{01}+\\ S_1\left(1-{\text{θ}}_i^{+}\right)S_1\left({\text{θ}}_h^{+}\right)I_{10}\left(x\right)+S_1\left(1-{\text{θ}}_i^{+}\right)S_1\left(1-{\text{θ}}_h^{+}\right)I_{11}\left(x\right)\end{array}$ wherein $I\left({\theta }_i^{+},{\theta }_h^{+},x\right)$ is the interpolated intensity of a pixel with local coordinates ${\theta }_i^{+},{\theta }_h^{+},x;$ $S_1\left({\text{θ}}_n^{+}\right)$ is the value of the smoothstep function at local coordinate ${\theta }_n^{+};$ I.sub.ab(x) is the value of the pixel intensity of neighboring texture image ab at pixel location x.

5. The method of claim 1, wherein the texture images are sRGB texture images.

6. The method of claim 1, wherein the BTF has been generated by a method comprising at least the following steps: measuring an initial BTF for the paint using a camera-based measurement device, capturing spectral reflectance data for the paint for a pre-given number of different measurement geometries using a spectrophotometer, and adapting the initial BTF to the captured spectral reflectance data, thus gaining an optimized BTF.

7. The method of claim 6, wherein the camera-based measurement device creates a plurality of images of the object at different viewing angles, at different illumination angles, for different illumination colors and/or for different exposure times, thus providing a plurality of measurement data considering a plurality of combinations of illumination angle, viewing angle, illumination color and/or exposure time.

8. The method of claim 7, wherein the images with different illumination color and different exposure time, but with equal illumination angle and viewing angle are combined to images with high dynamic range, respectively.

9. The method of claim 6, wherein the initial BTF is segmented into two main terms, a first term being a homogeneous bi-directional reflectance distribution function (BRDF) which describes reflectance properties of the object depending only on the measurement geometry and the second term being a texture function which accounts for a spatially varying appearance of the object.

10. A computer system comprising: a computer unit; a computer readable program with program code stored in a non-transitory computer-readable storage medium, the program code causing the computer unit, when the program is executed on the computer unit, to use a bi-directional texture function (BTF) of a paint comprising effect pigments to generate a representation of an object coated with the paint which accurately reproduces the visual appearance of the object at a given viewing and illumination direction of the object, the representation generated using a 3D render engine which interpolates a texture image at the given viewing and illumination direction from texture images present in the BTF representing neighboring viewing and illumination directions using a smoothstep function $S_1\left(x\right)={\text{S}}_1\left({\text{x}}^{+}\left({\text{x}}^{\ast },{\text{t}}_{\text{n}},\text{w}\right)\right)={\text{S}}_1\left(\frac{{\text{x}}^{\ast }-{\text{t}}_{\text{n}}+\frac{\text{w}}{2}}{\text{w}}\right)$ in an interval with width w around a random transition point t .sub.n at the local coordinate x*.

11. The computer system of claim 10, wherein the render engine is a real-time render engine.

12. The computer system of claim 10, further comprising a shader for the render engine.

13. The computer system of claim 12, wherein the shader comprises a fragment shader and a vertex shader.

14. The computer system of claim 12, further comprising an importer for the shader.

15. The computer system of claim 14, wherein the importer is configured to read the BTF from a file and translate the parameters of the BTF to the parameters of a texture function used by the shader.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] FIG. 1 shows an image interpolated by linear interpolation (middle) of two exemplary texture images (left, right), and the corresponding intensity histogram (bottom);

[0100] FIG. 2 shows an image interpolated using the interpolation scheme of the present disclosure (middle) from the exemplary texture images (left, right) of FIG. 1, and the corresponding intensity histogram (bottom).

DETAILED DESCRIPTION OF THE DRAWINGS

[0101] FIG. 1 shows two exemplary texture images (Texture A, Texture B) of a car paint comprising sparkle pigments. The image in the top center (Interpolated Texture) has been generated from Texture A and Texture B by linear interpolation.

[0102] The corresponding intensity histogram of the images is shown in the lower part of FIG. 1. In each bar of the histogram, the number of pixels having a given intensity is displayed. Each bar is comprised of three columns representing, from left to right, the values for Texture A, Texture B, and the Interpolated Texture, respectively. The histogram clearly shows the reduced contrast of the linearly interpolated texture image.

[0103] FIG. 2 again shows the two exemplary texture images (Texture A, Texture B) of FIG. 1. The image in the top center (Interpolated Texture) has been generated from Texture A and Texture B by the interpolation scheme of the present disclosure.

[0104] The corresponding intensity histogram of the images is shown in the lower part of FIG. 2. As in FIG. 1, each bar of the histogram is comprised of three columns representing, from left to right, the values for Texture A, Texture B, and the Interpolated Texture, respectively. The histogram clearly shows that contrast and intensity gradient are preserved in the interpolated image.