Fast and accurate 3d rendering of automotive coatings

CI C23, Darmstadt, Germany, October 19-23, 2015The color of automot ve coat ngs var es w th llum nat on and detect on angles. For 3D render ng of these coat ngs currently two categor es of methods ex st, a m ng at e ther color accuracy or at computat onal speed. Current methods that a m for color accuracy are based on measurement data from BRDF nstruments. Since many hundreds of measurement geometr es are needed to capture the color var at on w th angles, these methods requ re t me-expens ve nterpolat on of large three-d mensional Look-Up Tables. Current methods that aim for computational speed use physically crude approximations, usually taking into account color variations with respect to only one of the four angular dimensions. Here, we derive a new approach for 3D rendering of automotive and other gonio-apparent coatings, which is a dedicated form of microfacet models. It aims at improved color accuracy as compared to the current computationally inexpensive methods, combined with higher computational speed and lower cost as compared to current color-accurate rendering techniques. The new approach utilizes a recently developed physical analysis method, introducing flake-based parameters and isochromatic lines, for the reflection properties of automotive coatings. This makes it more accurate than current fast rendering methods. The new method naturally leads to two- rather than three-dimensional Look-up Tables, which explains the small computation time it needs. We show that when applied to 3D rendering, this method indeed leads to accurate 3D rendering of automotive coatings while requiring reduced computation times. For numerical errors found in some special cases, solutions are found and tested.Peer Reviewe