Improving 3D reconstruction accuracy in wavelet transform profilometry by reducing shadow effects

Abstract

Wavelet transform profilometry is a three‐dimensional (3D) reconstruction method based on the structured light technique of fringe pattern projection, widely used because it is a non‐invasive, high‐performance 3D reconstruction method. The presence of shadows created by the object in the image capture process is an obstacle in obtaining accurate 3D reconstructions, as they add noise to the phase data, leading to artefacts in object reconstruction, even when using robust phase‐unwrapping algorithms. Since shadows present diverse intensities and shapes, detecting and eliminating their effects are challenging tasks. This work presents a novel method to detect shadow regions and reduce their effects in 3D reconstruction. The proposed method uses coloured fringe patterns to detect the shadows and mathematical morphology to condition the outlines of the shadow regions. The shadow outline information is used to interpolate the background‐plane fringe pattern onto the captured scene, where the shadows are detected. The mean squared error (MSE) of the reconstructed objects is reduced to 25% of the MSE without shadow removal, on an average, when using the Bioucas phase‐unwrapping method. When using the Ghiglia phase‐unwrapping method, the MSE reduction is to 8.3%, on an average, of the MSE in the shadow case.