A pre-processing method for the fringe image in phase measuring profilometry

The measurement system currently used in Phase Measuring Profilometry(PMP) consists of a Digital Light Projector(DLP), a CCD camera, and a computer system. However, the inherent gamma nonlinearity of the DLP and CCD camera can affect the output with a nonsinusoidal fringe image. In the same tine the systematic noise is an important error source. Some conventional filtering algorithms may either make the fringe more blurring or be inefficient for fringe images. Eventually, the obtained fringe image is non-sinusoidal and with systematic random noise inevitably. Aimed at these problems, a pre-processing method for the fringe image is presented in this paper. Firstly, an anti-deforming light model is designed and then projected by the DLP. Through the gamma nonlinear response of the whole system, the waveform is corrected. Secondly, an improved orientation filter-based method is designed to overcome the systematic random noise and can achieve better effect than other algorithm does. Experiment, according to aforementioned two steps, is carried out and preferable fringe images can be gained. The fringe waveform is more close to the ideal sinusoidal wave. Also the systematic noise is reduced effectively while the fringe image is still clear. In the paper, two steps of this method are detailed and some experimental results are also reported.