Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / image-1.0.15 / imnoise.m

diff --git a/octave_packages/image-1.0.15/imnoise.m b/octave_packages/image-1.0.15/imnoise.m
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+## Copyright (C) 2000 Paul Kienzle
+##
+## 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 2 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, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{B} =} imnoise (@var{A}, @var{type})
+## Adds noise to image in @var{A}.
+##
+## @table @code
+## @item imnoise (A, 'gaussian' [, mean [, var]])
+## additive gaussian noise: @var{B} = @var{A} + noise
+## defaults to mean=0, var=0.01
+## @item  imnoise (A, 'salt & pepper' [, density])
+## lost pixels: A = 0 or 1 for density*100% of the pixels
+## defaults to density=0.05, or 5%
+## @item imnoise (A, 'speckle' [, var])
+## multiplicative gaussian noise: @var{B} = @var{A} + @var{A}*noise
+## defaults to var=0.04
+## @end table
+## @end deftypefn
+
+## Modified: Stefan van der Walt <stefan@sun.ac.za>, 2004-02-24
+
+function A = imnoise(A, stype, a, b)
+
+  if (nargin < 2 || nargin > 4 || !ismatrix(A) || !ischar(stype))
+    usage("B = imnoise(A, type, parameters, ...)");
+  endif
+  
+  valid = (min(A(:)) >= 0 && max(A(:)) <= 1);
+
+  stype = tolower(stype);
+  if (strcmp(stype, 'gaussian'))
+    if (nargin < 3), a = 0.0; endif
+    if (nargin < 4), b = 0.01; endif
+    A = A + (a + randn(size(A)) * sqrt(b));
+    ## Variance of Gaussian data with mean 0 is E[X^2]
+  elseif (strcmp(stype, 'salt & pepper'))
+    if (nargin < 3), a = 0.05; endif
+    noise = rand(size(A));
+    A(noise <= a/2) = 0;
+    A(noise >= 1-a/2) = 1;
+  elseif (strcmp(stype, 'speckle'))
+    if (nargin < 3), a = 0.04; endif
+    A = A .* (1 + randn(size(A))*sqrt(a));
+  else
+    error("imnoise: use type 'gaussian', 'salt & pepper', or 'speckle'");
+  endif
+  
+  if valid
+    A(A>1) = 1;
+    A(A<0) = 0;
+  else
+    warning("Image should be in [0,1]");
+  endif
+
+endfunction
+
+%!assert(var(imnoise(ones(10)/2,'gaussian')(:)),0.01,0.005) # probabilistic
+%!assert(length(find(imnoise(ones(10)/2,'salt & pepper')~=0.5)),5,10) # probabilistic
+%!assert(var(imnoise(ones(10)/2,'speckle')(:)),0.01,0.005) # probabilistic