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frandphase

$ \bigcirc$Name


frandphase Phase Randomization of a Fimage




$ \bigcirc$Command Synopsis


frandphase [-i] in out



-i : in order NOT to reinitialize the random seed

in : input Fimage

out : output Fimage




$ \bigcirc$Function Summary


void frandphase (in , out , i_flag )

Fimage in , out ;

char *i_flag ;




$ \bigcirc$Description


This module performs a ``phase randomization'' on a Fimage, defined by

u' = F-1{| F{u}| ei$\scriptstyle \phi$},

where F{u} means the Fourier Transform of u, and $ \phi$ is an antisymetric field of random independant variables uniformely distributed on [0, 2$ \pi$[. In addition to that, a gain-offset correction is finally applied on u' in order to keep the u's original mean and variance.

This operator can be viewed as a ``texturization'', since it is well-known that microscopic textures can be caracterized by their correlation function

$\displaystyle \Gamma_{u}^{}$(x) = < u(t)u(t + x) > t,

which Fourier Transform equals | F{u}|2 up to a multiplicative coefficient (Wiener-Kichnine theorem). Thus, this function is a kind of projection on the space of microscopic textures.

The random seed used (drand48) is reinitialized with the current time unless the -i option is set.

NB: Calling this C-subroutine with out = in is possible




$ \bigcirc$See Also


faxpb, fft2d, fmean, fvar.




$ \bigcirc$Version 1.2


Last Modification date : Thu Apr 10 15:34:47 2003


$ \bigcirc$Author


Lionel Moisan






next up previous contents index
Next: fshrink2 Up: Reference Previous: fhamming   Contents   Index
mw 2004-05-05