/usr/share/octave/packages/signal-1.3.0/xcorr2.m is in octave-signal 1.3.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 | ## Copyright (C) 2000 Dave Cogdell <cogdelld@asme.org>
## Copyright (C) 2000 Paul Kienzle <pkienzle@users.sf.net>
## Copyright (C) 2012 Carnë Draug <carandraug+dev@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; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} xcorr2 (@var{a})
## @deftypefnx {Function File} {} xcorr2 (@var{a}, @var{b})
## @deftypefnx {Function File} {} xcorr2 (@dots{}, @var{scale})
## Compute the 2D cross-correlation of matrices @var{a} and @var{b}.
##
## If @var{b} is not specified, computes autocorrelation of @var{a}, i.e.,
## same as @code{xcorr (@var{a}, @var{a})}.
##
## The optional argument @var{scale}, defines the type of scaling applied to the
## cross-correlation matrix. Possible values are:
##
## @table @asis
## @item "none" (default)
## No scaling.
##
## @item "biased"
## Scales the raw cross-correlation by the maximum number of elements of @var{a}
## and @var{b} involved in the generation of any element of @var{c}.
##
## @item "unbiased"
## Scales the raw correlation by dividing each element in the cross-correlation
## matrix by the number of products @var{a} and @var{b} used to generate that
## element.
##
## @item "coeff"
## Scales the normalized cross-correlation on the range of [0 1] so that a value
## of 1 corresponds to a correlation coefficient of 1.
## @end table
##
## @seealso{conv2, corr2, xcorr}
## @end deftypefn
function c = xcorr2 (a, b, biasflag = "none")
if (nargin < 1 || nargin > 3)
print_usage;
elseif (nargin == 2 && ischar (b))
biasflag = b;
b = a;
elseif (nargin == 1)
## we have to set this case here instead of the function line, because if
## someone calls the function with zero argument, since a is never set, we
## will fail with "`a' undefined" error rather that print_usage
b = a;
endif
if (ndims (a) != 2 || ndims (b) != 2)
error ("xcorr2: input matrices must must have only 2 dimensions");
endif
## compute correlation
[ma,na] = size(a);
[mb,nb] = size(b);
c = conv2 (a, conj (b (mb:-1:1, nb:-1:1)));
## bias routines by Dave Cogdell (cogdelld@asme.org)
## optimized by Paul Kienzle (pkienzle@users.sf.net)
## coeff routine by Carnë Draug (carandraug+dev@gmail.com)
switch lower (biasflag)
case {"none"}
## do nothing, it's all done
case {"biased"}
c = c / ( min ([ma, mb]) * min ([na, nb]) );
case {"unbiased"}
lo = min ([na,nb]);
hi = max ([na, nb]);
row = [ 1:(lo-1), lo*ones(1,hi-lo+1), (lo-1):-1:1 ];
lo = min ([ma,mb]);
hi = max ([ma, mb]);
col = [ 1:(lo-1), lo*ones(1,hi-lo+1), (lo-1):-1:1 ]';
bias = col*row;
c = c./bias;
case {"coeff"}
a = double (a);
b = double (b);
a = conv2 (a.^2, ones (size (b)));
b = sumsq (b(:));
c(:,:) = c(:,:) ./ sqrt (a(:,:) * b);
otherwise
error ("xcorr2: invalid type of scale %s", biasflag);
endswitch
endfunction
%!test # basic usage
%! a = magic (5);
%! b = [6 13 22; 10 18 23; 8 15 23];
%! c = [391 807 519 391 473 289 120
%! 920 1318 1045 909 1133 702 278
%! 995 1476 1338 1534 2040 1161 426
%! 828 1045 1501 2047 2108 1101 340
%! 571 1219 2074 2155 1896 821 234
%! 473 1006 1643 1457 946 347 108
%! 242 539 850 477 374 129 54];
%! assert (xcorr2 (a, b), c);
%!shared a, b, c, row_shift, col_shift
%! row_shift = 18;
%! col_shift = 20;
%! a = randi (255, 30, 30);
%! b = a(row_shift-10:row_shift, col_shift-7:col_shift);
%! c = xcorr2 (a, b, "coeff");
%!assert (nthargout ([1 2], @find, c == max (c(:))), {row_shift, col_shift}); # should return exact coordinates
%! m = rand (size (b)) > 0.5;
%! b(m) = b(m) * 0.95;
%! b(!m) = b(!m) * 1.05;
%! c = xcorr2 (a, b, "coeff");
%!assert (nthargout ([1 2], @find, c == max (c(:))), {row_shift, col_shift}); # even with some small noise, should return exact coordinates
%!test # coeff of autocorrelation must be same as negavtive of correlation by additive inverse
%! a = 10 * randn (100, 100);
%! auto = xcorr2 (a, "coeff");
%! add_in = xcorr2 (a, -a, "coeff");
%! assert ([min(auto(:)), max(auto(:))], -[max(add_in(:)), min(add_in(:))]);
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