This module adds Gaussian noise of standart deviation $sd$ (default value~:
10.0) to a Cmovie, using the {\sf fganoise} module.

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The random seed is reinitialized once at the begining, but not for each 
image of the movie (which could create correlations between successive
images).

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