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1 ## Copyright (C) 2000 Paul Kienzle |
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2 ## |
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3 ## This program is free software; you can redistribute it and/or modify |
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4 ## it under the terms of the GNU General Public License as published by |
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5 ## the Free Software Foundation; either version 2 of the License, or |
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6 ## (at your option) any later version. |
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7 ## |
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8 ## This program is distributed in the hope that it will be useful, |
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9 ## but WITHOUT ANY WARRANTY; without even the implied warranty of |
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10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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11 ## GNU General Public License for more details. |
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12 ## |
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13 ## You should have received a copy of the GNU General Public License |
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14 ## along with this program; if not, write to the Free Software |
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15 ## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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16 |
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17 ## usage: B = imnoise (A, type) |
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18 ## |
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19 ## Adds noise to image in A. |
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20 ## |
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21 ## imnoise (A, 'gaussian' [, mean [, var]]) |
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22 ## additive gaussian noise: A = A + noise |
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23 ## defaults to mean=0, var=0.01 |
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24 ## |
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25 ## imnoise (A, 'salt & pepper' [, density]) |
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26 ## lost pixels: A = 0 or 1 for density*100% of the pixels |
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27 ## defaults to density=0.05, or 5% |
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28 ## |
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29 ## imnoise (A, 'speckle' [, var]) |
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30 ## multiplicative gaussian noise: A = A + A*noise |
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31 ## defaults to var=0.04 |
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32 |
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33 function A = imnoise(A, stype, a, b) |
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34 |
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35 if (nargin < 3 || nargin > 4 || !is_matrix(A) || !isstr(stype)) |
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36 usage("B = imnoise(A, type, parameters, ...)"); |
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37 endif |
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38 |
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39 stype = tolower(stype); |
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40 if (strcmp(stype, 'gaussian')) |
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41 if (nargin < 3), a = 0.0; endif |
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42 if (nargin < 4), b = 0.01; endif |
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43 A = A + (a + randn(size(A)) * b); |
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44 elseif (strcmp(stype, 'salt & pepper')) |
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45 if (nargin < 3), a = 0.05; endif |
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46 noise = rand(size(A)); |
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47 A(noise <= a/2) = 0; |
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48 A(noise >= 1-a/2) = 1; |
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49 elseif (strcmp(stype, 'speckle')) |
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50 if (nargin < 3), a = 0.04; endif |
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51 A = A * (1 + randn(size(A))*a); |
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52 else |
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53 error("imnoise: use type 'gaussian', 'salt & pepper', or 'speckle'"); |
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54 endif |
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55 |
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56 endfunction |
