Wavelet analysis for shadow detection in Fringe Projection Profilometry

Fringe Projection Profilometry (FPP) is the most widely used method for 3D reconstruction. In FPP, the elevation information is deduced from the deformation of the pattern induced by the object. In the shadow areas, no fringe patterns are formed and as a result, the elevation information in these areas cannot be determined resulting in errors in the 3D reconstruction. This paper proposes a new method to detect the occurrences of shadow using the Haar Wavelet for a typical single camera with one projector configuration. The Haar wavelet emphasises the sudden change caused by boundary of the shadow and also shows the non-existence of the pattern in the shadow area. The method detects shadow boundary and differentiates shadow and non-shadow area based on the threshold defined from the statistics of the signal. The method is found more suitable for deformed fringe pattern than Fourier-based shadow detection, as the nature of the signal is non-stationary. The proposed method correctly detects shadow with robustness to the noise power up to 16.9 dB.