Fixed-focus laser triangulation simultaneously measures the morphology and color of object

Abstract Simultaneously measuring the surface morphology and color of a sample is crucial for full-color 3D printing and digitization of cultural artifacts. However, traditional methods are susceptible to the variations in the measurement angle and illumination condition, making it difficult to balance the color fidelity and spatial accuracy. Here, we propose a laser triangulation method that is implemented with a fixed focus, dark-field illumination, and data-driven spectral classification. With a fixed focus, this method measures the height of surface by analyzing the shape of reflected light spot. The dark-field illumination diminishes the background contributed by the specular reflection of white light, enabling an accurate spectral measurement. The data-driven spectral classification algorithm establishes color dataset for each sample, and ensures a precise color recognition through principal component analysis dimensionality reduction and K-nearest neighbor classification. In our experiment, this method achieved an axial resolution of 5.1 μm. The color classification accuracy was as high as 99.79% on ColorChecker cards and 96.03% on Pantone color match cards. Three samples were reconstructed and evaluated to validate this method, the mean absolute error of the morphology measurements did not exceed 25 μm, and the color difference (CIE2000) does not exceed 1.0, confirming its ability to accurately measure the surface morphology and color simultaneously.