Estimates the noise standard deviation from an (MRI) image (2D) corrupted with Rician noise based on the skewness of the distribution. This method doesn't depend on the background for noise estimation. Can be used for MR images with and without background.
Ref: Jeny Rajan, Dirk Poot, Jaber Juntu and Jan Sijbers, "Noise measurement from magnitude MRI using local estimates of variance and skewness", Physics in Medicine and Biology, Vol 55, N441-N449,2010.
adding BSD license
added the polynomial expression of the lookup table mentioned in the program.