introduction
In the luxury car market, decorative materials offer an increasing array of possibilities. Varnished wood is a commonly used material, but it has certain limitations such as wear, scratches, and ultraviolet aging, which require maintenance. As a solution, specific finishes can be applied to avoid the above-mentioned degradation.
In this article, we will demonstrate how the appearance of wood evolves depending on the finish applied: raw or varnished. And the methods used to represent these optical behaviors.
图 1 - Wood Ocean™ 模拟
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When creating material models for optical applications, it is crucial to consider both the volume properties (such as dielectric functions) and the surface characteristics (such as reflectivity). Taking into account surface texture, the visible grain patterns of certain materials, such as wood, can be particularly challenging to reproduce. In fact, random patterns may sometimes cover the entire surface, and due to size limitations (typical acceptable sample sizes are often up to 15 cm), traditional measurement equipment cannot be used for physical characterization.
Another method involves measuring a portion of the grain and using a process known as "tilling" to repeat the pattern across a large-scale surface. However, the repetition of this pattern is often visible.
Figure 2-1 - Good tilling due to the use of a pattern with too much repetition
Figure 2-2 - Poor tilling due to the use of a pattern with too much repetition
To bypass this issue, Eclat Digital developed a specialized method to simulate this anarchic patterned material. By combining the specific skills of engineers (measurement and characterization) and graphic designers (texture), the large-scale randomness of the material can be considered when running light tracing simulations using Ocean™.
More specific information and case studies on this simulation process can be found elsewhere.
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https://eclat-digital.com/materials-in-virtual-world/
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https://eclat-digital.com/rd-and-graphic-design-collaboration-for-ocean-project/
Woodcraft
To circumvent the limitations of sample size, we will create wood textures using Substance Designer.
We will create a so-called "procedural" texture. With the aid of pattern tools, noise, and arithmetic functions, we can create patterns that are infinitely repeatable without any size constraints, thus eliminating any visible repetition.
How does it work?
First, we will learn how to represent wood fibers using patterns and filters. Then, the results of this work will be used to set the chromatography of the wood.
The goal is to have something that is repeatable, accurate, and consistent with the reality represented by the actual sample. If a higher resolution version of this material is needed in the future, due to the use of procedural textures, it can always be recreated.
The goal is to have something that is repeatable, accurate, and consistent with the reality represented by the actual sample. If a higher resolution version of this material is needed in the future, due to the use of procedural textures, it can always be recreated.
Figure 3 - Low-frequency procedural pattern - data used to simulate the behavior of light on the surface of the material.
Figure 4 - Modifying and separating the fine structure of the wood to receive color information. On the right side of the chart, the separated parts are mixed to recreate the complete wood diffuse color.
Figure 5 - Wood texture with diffuse color result.
Now, we will delve into the detailed treatment of each type of wood: Surface Treatment: Raw and Varnished.
Raw Wood
We start with the texture described above and add scattering optical properties (BRDF, more information in this article: https://eclat-digital.com/introduction-to-material-measurements-from-theory-to-rendering/), supported by measurements using a goniophotometer. We will find a treatment method for the wood that gives it a slight gloss (polished, wood color?) and the color is not very saturated. We also notice that roughness diffuses light, which often makes the chromaticity of the wood whiter.
Figure 6 - The micro-roughness of the wood greatly diffuses the light and reduces the average chromaticity of the wood.
To validate this hypothesis, we simply need to moisten the wood with a thin layer of water, which fills the microscopic roughness, making it smooth, and the color will greatly darken.
Figure 7 - The water film fills the roughness, eliminating the roughness's impact, and the "true" color of the wood is observed.
Varnished Wood
This case is the most complex. Because varnish introduces different effects to consider.
Firstly, the varnish will produce the same effect as the water film described in the previous section: the varnish fills the roughness of the wood and darkens the average color.
However, here we consider a slightly worn varnish. Therefore, we introduce the defects previously characterized on physical samples: polishing, micro-scratches, scratches, and the "orange peel effect" caused by the drying of the varnish. This effect is usually very noticeable in car paint and produces small ripples in the reflection.
Figure 8 - Even though the varnish fills the roughness and darkens the color, a few defects in the varnish will very slightly diffuse the light and enhance the overall brightness.
These micro-roughnesses are created with the help of black and white images, and Ocean uses these images to simulate areas of higher or lower on the material's surface, thereby changing the surface conditions.
图 9 - 划痕和清漆微图案的高度黑白数据
Simulated images in vehicles.
We used all of the above to simulate the decoration of different finishes on the dashboard in a vehicle: raw and varnished.
Figure 10 - Raw Wood. We notice a slight sheen on the light areas and in the corners.
Figure 11 - Varnished Wood. The varnish fills the roughness, making the color deeper. However, the surface of the varnish is slightly brighter. Left: Micro-scratches. Right: Orange peel effect making the reflection ripple.
This is our most advanced optical simulation technology. If you want to know more, please contact us directly.
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原文始发于微信公众号（视觉仿真实验室）：更精细的模拟—汽车内饰木饰面光学仿真
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