Underwater 3D shape reconstruction by fringe projection - CAA

Hallo everybody!

Sorry for the long time...

My second fovourite presentatiton was from CAA: "Underwater 3D shape reconstruction by fringe projection"
Great research at the University of Calabria, Italy (Bianco, G., Bruno, F., Muzzupappa, M., Luchi, M.L.).
Our Institute accomplished a big camera calibration project for underwater archaeological documentation, which was an interesting topic.


Part of Introcuction:

"....In this work, we have tested the effectiveness of a
whole-field structured light technique, based on
fringe projection, in underwater environment. The
Fringe Projection Technique (FPT) is widely used in
air (RASTOGI and GORTHI, 2010), and consists of
projection and acquisition of sinusoidal patterns on
the object (in the simplest case, one pattern is
enough). The system is composed by a video
projector and a digital camera, and the geometrical
setup is based on the principle of optical
triangulation. The recorded images are analyzed to
evaluate the phase-map of the object - which contains
the height information - with a signal processing
technique such as Fourier Transform (FT) , Wavelet
Transform (WT) , Windowed Fourier Transform
(WFT) , Spatial Phase Detection (SPD) or Phase
Stepping (PS). Any of these techniques of phase
measurement provides a discontinuous phase map of
the object (wrapped): so it becomes necessary to use
phase unwrapping in order to obtain a continuous
phase distribution (SURREL, 1998). By knowing the
intrinsic (focal distances, coordinates of the principal
points, and distortions) and extrinsic (relative
positions between the optical devises) parameters,
one can calculate the point clouds from the
triangulation between a optical ray of the camera (at
i,j pixel with phase value φi,j) and the relative plane
in the projector frame at the same phase value...."