## Copyright (C) 2008 SÃ¸ren Hauberg ## ## This program is free software; you can redistribute it and/or modify ## it under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 3 of the License, or ## (at your option) any later version. ## ## This program is distributed in the hope that it will be useful, ## but WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ## GNU General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with this program; if not, write to the Free Software ## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA ## -*- texinfo -*- ## @deftypefn {Function File} {@var{S} =} stdfilt (@var{im}) ## @deftypefnx{Function File} {@var{S} =} stdfilt (@var{im}, @var{domain}) ## @deftypefnx{Function File} {@var{S} =} stdfilt (@var{im}, @var{domain}, @var{padding}, ...) ## Computes the local standard deviation in a neighbourhood around each pixel in ## an image. ## ## The standard deviation of the pixels of a neighbourhood is computed as ## ## @example ## @var{S} = sqrt ((sum (@var{x} - @var{mu}).^2)/(@var{N}-1)) ## @end example ## ## where @var{mu} is the mean value of the pixels in the neighbourhood, ## @var{N} is the number of pixels in the neighbourhood. So, an unbiased estimator ## is used. ## ## The neighbourhood is defined by the @var{domain} binary mask. Elements of the ## mask with a non-zero value are considered part of the neighbourhood. By default ## a 3 by 3 matrix containing only non-zero values is used. ## ## At the border of the image, extrapolation is used. By default symmetric ## extrapolation is used, but any method supported by the @code{padarray} function ## can be used. Since extrapolation is used, one can expect a lower deviation near ## the image border. ## ## @seealso{std2, paddarray, entropyfilt} ## @end deftypefn function retval = stdfilt (I, domain = true (3), padding = "symmetric", varargin) ## Check input if (nargin == 0) error ("stdfilt: not enough input arguments"); endif if (!ismatrix (I)) error ("stdfilt: first input must be a matrix"); endif if (!ismatrix (domain)) error ("stdfilt: second input argument must be a logical matrix"); endif domain = (domain > 0); ## Pad image pad = floor (size (domain)/2); I = padarray (I, pad, padding, varargin {:}); even = (round (size (domain)/2) == size (domain)/2); idx = cell (1, ndims (I)); for k = 1:ndims (I) idx {k} = (even (k)+1):size (I, k); endfor I = I (idx {:}); ## Perform filtering retval = __spatial_filtering__ (I, domain, "std", I, 0); endfunction

Generated by Doxygen 1.6.0 Back to index