Reflectance transformation imaging for characterizing bulk planar distribution of metal flakes in pigmented coating systems

Abstract The metal flakes’ (MFs) bulk planar distribution (BPD) quality is a key dimension in predicting the appearance of Metal flake-pigmented coatings (MF-PCs). This distribution influences their meso-appearance (mottling) and micro-appearance (visual texture). To address this, the study utilized a dome-based reflectance transformation imaging (DB-RTI) system to capture the intensity (monochromatic) multi-light image collections (I-MLICs) of MF-PC. These images were then processed to identify the positions of metal flakes based on their local angular reflections (LARn). The resultant stochastic point patterns (SPPs) were then analyzed using a stationary Poisson process (PP) as the null hypothesis, which characterizes their BPD quality regarding clustering, randomness, or regularity on a short-range scale. The proposed methodology effectively characterizes the BPD of metal flakes in MF-PCs, accounting for their type, size, count, and even variations in basecoat color. Some existing limitations of the RTI method in its current application, as well as some sources of error in the proposed algorithm, were also addressed.