Mercurial > hg > octave-image
changeset 277:02b11f5cf655
Added radon transformation
author | hauberg |
---|---|
date | Thu, 06 Mar 2008 11:48:17 +0000 |
parents | e7355884e532 |
children | 8218c2337178 |
files | INDEX inst/radon.m |
diffstat | 2 files changed, 89 insertions(+), 0 deletions(-) [+] |
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--- a/INDEX +++ b/INDEX @@ -47,6 +47,7 @@ stretchlim makelut applylut deriche + radon Black and white image functions bwarea bwdist
new file mode 100644 --- /dev/null +++ b/inst/radon.m @@ -0,0 +1,88 @@ +## Copyright (C) 2007 Alexander Barth <barth.alexander@gmail.com> +## +## +## 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; see the file COPYING. If not, see +## <http://www.gnu.org/licenses/>. + +## -*- texinfo -*- +## @deftypefn {Function File} {[@var{RT},@var{xp}] =} radon(@var{I}, @var{theta}) +## @deftypefnx {Function File} {[@var{RT},@var{xp}] =} radon(@var{I}) +## +## Calculates the 2D-Radon transform of the matrix @var{I} at angles given in +## @var{theta}. To each element of @var{theta} corresponds a column in @var{RT}. +## The variable @var{xp} represents the x-axis of the rotated coordinate. +## If @var{theta} is not defined, then 0:179 is assumed. +## @end deftypefn + + +function [RT,xp] = radon (I,theta) + + ## Input checking + if (nargin == 0 | nargin > 2) + print_usage (); + elseif (nargin == 1) + theta = 0:179; + endif + + if (!ismatrix(I) || ndims(I) != 2) + error("radon: first input must be a MxN matrix"); + endif + + if (!isvector(theta)) + error("radon: second input must be a vector"); + endif + + [m, n] = size (I); + + # center of image + xc = floor ((m+1)/2); + yc = floor ((n+1)/2); + + # divide each pixel into 2x2 subpixels + + d = reshape (I,[1 m 1 n]); + d = d([1 1],:,[1 1],:); + d = reshape (d,[2*m 2*n])/4; + + b = ceil (sqrt (sum (size (I).^2))/2 + 1); + xp = [-b:b]'; + sz = size(xp); + + [X,Y] = ndgrid (0.75 - xc + [0:2*m-1]/2,0.75 - yc + [0:2*n-1]/2); + + X = X(:)'; + Y = Y(:)'; + d = d(:)'; + + th = theta*pi/180; + + for l=1:length (theta) + # project each pixel to vector (-sin(th),cos(th)) + Xp = -sin (th(l)) * X + cos (th(l)) * Y; + + ip = Xp + b + 1; + + k = floor (ip); + frac = ip-k; + + RT(:,l) = accumarray (k',d .* (1-frac),sz) + accumarray (k'+1,d .* frac,sz); + endfor + +endfunction + +%!test +%! A = radon(ones(2,2),30); +%! assert (A,[0 0 0.608253175473055 2.103325780167649 1.236538105676658 0.051882938682637 0]',1e-10) + +