
The Spiral Phase Transform ◾ 131
4.3.2 Orientation and Direction Estimation
e simplest implementation of the SPT does not require estimation of the
fringe orientation. Without orientation or direction, it is still possible to esti-
mate the absolute value of the quadrature sine wave using Equation (4.19).
To disentangle the underlying structure of fringe phase, it is necessary
to know, or at least estimate, the fringe direction. Returning to the interfer-
ometric fringe pattern in Equation (4.1), there is an assumption that there
is an underlying phase pattern ψ(x,y). e direction vector associated with
the gradient of this 2-D scalar fu ...