Normal-Based Bas-Relief Modelling via Near-Lighting Photometric Stereo

We present a near-lighting photometric stereo (NL-PS) system to produce digital bas-reliefs from a physical object (set) directly. Unlike both the 2D image and 3D model-based modelling methods that require complicated interactions and transformations, the technique using NL-PS is easy to use with cost-effective hardware, providing users with a trade-off between abstract and representation when creating bas-reliefs. Our algorithm consists of two steps: normal map acquisition and constrained 3D reconstruction. First, we introduce a lighting model, named the quasi-point lighting model (QPLM), and provide a two-step calibration solution in our NL-PS system to generate a dense normal map. Second, we filter the normal map into a detail layer and a structure layer, and formulate detail- or structure-preserving bas-relief modelling as a constrained surface reconstruction problem of solving a sparse linear system. The main contribution is a WYSIWYG (i.e. what you see is what you get) way of building new solvers that produces multi-style bas-reliefs with their geometric structures and/or details preserved. The performance of our approach is experimentally validated via comparisons with the state-of-the-art methods.