N-step color phase-shifting method for 3D shape measurement

This thesis proposes a N-step color phase-shifting method for measuring 3D shape of objects. Firstly, color fringe patterns are designed and projected onto the object surface by a projector. Distorted fringe patterns on the object surface are captured by two digital cameras, and intensities of each pixel in the red, green and blue channels are obtained from the captured color images. Phase values of all pixels are calculated by the phase-shifting method from the obtained RGB intensities. At the same time, phase errors are also corrected by using a phase error look-up-table and a RGB look-up-table. Then, the phase-unwrapping technique is applied to convert phase values to the height of the object surface. In the phase-unwrapping process, both the branch cut algorithm and the quality-guided algorithm are included to improve the quality of shape reconstruction. Data registration and integration are performed to unify 3D data points obtained from two cameras. Finally, an integrated program is developed by combing phase-shifting process, phase-unwrapping process, data registration, and data integration. With the developed program, several measurement examples are investigated. From the measurement results, it shows that the proposed method can reduce measurement errors effectively.