A novel technique using color-encoded stripes embedded into a sinusoidal fringe pattern for finding the absolute shape of an object is proposed. Phases of the projected fringes on the surface are evaluated by Fourier transform method. Unwrapping is then performed with reference to the color-encoded stripes. When surfaces of interest contain large depth discontinuities, the color-encoded stripes can easily identify the fringe order. Compared with other phase unwrapping schemes, this method offers many major advantages, including: (1) very low computation cost for the 3D reconstruction, (2) reliable phase unwrapping to complex objects, especially for surfaces with large depth discontinuities, (3) only one-shot measurement is required, and (4) robust performance to analyze dynamic objects.
We present a discussion on how an area-encoded fringe pattern is applied to describe the 3D shape of objects that have spatially isolated surfaces. Phases of the fringes can be carried out without ambiguity to retrieve the 3D shape. Compared with conventional fringe projection techniques, the proposed scheme is relatively reliable and robust to identify the fringe order. Only one phase measurement is required. This makes it possible to analyze dynamic objects.
An improved method is proposed to perform calibration-based fringe projected profilometry using a two-frequency fringe pattern for the 3D shape measurements of objects with large discontinuous height steps. A fabrication scheme for the two-frequency pattern is described as well. The proposed method offers following major advantages: (1) only one phase measurement needed for operation, (2) easiness for calibration, (3) robust performance, especially for automatic phase unwrapping, and (4) more flexible data acquisition for complex objects. This makes it possible for a single-shot measurement of dynamic objects with discontinuities. Both theoretical descriptions and experimental demonstrations are provided.
A supramolecular system stabilized through complementary hydrogen bonding and displaying stimuli-responsive behavior has been fabricated into “recordable” and “rewritable” surface relief gratings operated under laser illumination.
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