Absolute phase analysis method for three-dimensional surface profilometry using frequency-modulated grating

The authors propose a new high-speed and accurate phase analysis and subsequent phase unwrapping method for grating projection surface profilometry. In the proposed method, a special grating pattern is used for the projection. The light intensity distribution of this grating pattern has a form of a frequency modulated sinusoidal wave. In this grating pattern, two different phase distributions are included. The frequency modulated grating, which can be generated with an LCD projector or a film projector easily, is projected onto an object. Then, nine frames with phase stepping at a regular interval for a cycle are taken by a CCD camera. From these nine pictures, the two wrapped phase distributions are analyzed simultaneously. Then, using these phase distributions, phase unwrapping is carried out at each pixel independently. The 3-D profile of the object can be reconstructed using the absolute phase distribution. Since this method is suitable for high-speed shape measurement, applications to various inspections and 3-D surface digitizing are expected. (C) 2003 Society of Photo-Optical Instrumentation Engineers.