3D profile measurement based on estimation of spatial shifts between intensity ratios from multiple-step triangular patterns

This paper presents a multiple-step triangular-pattern spatial shift estimation approach for 3D object profilometry measurement. The proposed technique is based on the intensity ratio maps, but, compared to existing intensity ratio approaches, it employs spatial shift estimation to work out the 3D shape. The spatial shift is determined by making use of the inverse function of the intensity ratio map obtained from the reference plane, which is obtained by the least-square polynomial fitting technique. In contrast to existing intensity ratio approaches, the proposed method does not suffer from the influence of the nonlinear distortion associated with digital projection. Also, compared to the existing phase shifting method with phase error correction, the proposed technique is simple and thus is more suitable for fast measurement. The performance of the proposed technique has been tested and the advantages have been demonstrated by experiments.

► Identifying weakness of existing method for intensity ratio to height conversion.
► Using inverse function method to get spatial shift between two intensity ratios.
► Using branch-cut method for unwrapping the intensity ratios.