Absolute phase fingerprint matching in fringe projection profilometry based on chirped phase-shifted fringes.

Absolute phase computation is critical to fringe projection profilometry, yet temporal phase unwrapping requires additional patterns to encode absolute fringe order, degrading measurement efficiency. Spatial phase unwrapping eliminates additional patterns but yields only relative phase, making absolute height recovery impossible for isolated or discontinuous objects. To address this limitation, we propose an absolute phase fingerprint matching method based on chirped phase-shifted fringes. A set of chirped fringes is constructed by encoding absolute fringe order information directly into the fringe period such that the phase curvature varies monotonically. After spatial phase unwrapping, the relative phase of each isolated region is fingerprint matched to the global absolute phase. The unique curvature fingerprint enables precise regional localization within the global absolute phase space. Experimental results: plane RMS error of 0.0288 mm, standard sphere radius error of 0.0542 mm (relative error 0.0028%), and step height error of 0.0167 mm. These results demonstrate that the proposed chirped fringes achieve 3D measurement of isolated or discontinuous objects with accuracy comparable to the three-frequency heterodyne method, while reducing projected fringes from 12 to 4.