/usr/share/octave/packages/image-2.6.1/edgetaper.m is in octave-image 2.6.1-1.
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 | ## Copyright (C) 2015 Carnë Draug <carandraug@octave.org>
##
## 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} {} edgetaper (@var{img}, @var{psf})
## Blur border (edges) of image to prevent ringing artifacts.
##
## @emph{Warning}: this function is not @sc{Matlab} compatible and
## is likely to change in the future.
##
## @end deftypefn
function imgt = edgetaper (img, psf)
if (nargin != 2)
print_usage ();
elseif (! isnumeric (img))
error ("edgetaper: IMG must be numeric")
elseif (! isnumeric (psf))
error ("edgetaper: PSF must be numeric")
endif
img_size = size (img);
psf_size = size (psf);
n = max (numel (img_size), numel (psf_size));
img_size = postpad (img_size(:), n, 1);
psf_size = postpad (psf_size(:), n, 1);
## beware of psf_size = [16 16 1 8] paired with img_size [512 512 1 50]
## which are valid, singleton dimensions do not count for this check
if (any ((psf_size > (img_size / 2)) & (psf_size > 1)))
error ("edgetaper: PSF must be smaller than half of IMG dimensions")
endif
psf = psf ./ sum (psf(:)); # we use it for blurring so the sum must be 1
## FIXME this function is not Matlab compatible. I have no clue what
## Matlab is doing but is definitely not what they claim on the
## documentation. There are no references for the function and
## the documentation is sparse and incorrect.
##
## I have found papers that compare their method for reducing
## boundary artifacts against Matlab's edgetaper but even they
## do not comment it.
##
## It an implementation of edgetaper that is close to Matlab's
## documentation for the function. If anyone has patience, please
## fix this.
##
## Some questions about it:
##
## 1. the autocorrelation of the PSF is twice the size of the PSF
## but it will still be way smaller than the image. How can it be
## used to make a weighted mean between the blurred and the original
## image? We pretty much split it and only use it on the borders
## but looks like we end up with an image too blurred.
##
## 2. how do they blur the image? I will guess they pad the
## image but how?
##
## Note: always test this function with input as double precision
## since it returns the same class as input and may hide our
## differences.
blurred = fftconvn (img, psf, "same");
xpsf = normalized_autocorrelation (psf);
## The following will expand a ND matrix into a larger size
## repeating the center elements, e.g.,
##
## 1 2 2 2 3
## 1 2 3 4 5 5 5 6
## 4 5 6 => 4 5 5 5 6
## 7 8 9 4 5 5 5 6
## 7 8 8 8 9
## note the xpsf will always have odd sizes (2*psf_size +1)
xdims = ndims (xpsf);
xpsf_size = size (xpsf)(:);
idim = arrayfun (@(c, n, f) [1:c repmat(c, [1 n]) c:f], ceil (xpsf_size /2),
img_size(1:xdims) - xpsf_size -1, xpsf_size,
"UniformOutput", false);
subs = cell (xdims, 1);
[subs{:}] = ndgrid (idim{:});
inds = sub2ind (xpsf_size, subs{:});
weights = xpsf(inds);
imgt = (img .* weights) + (blurred .* (1 - weights));
imgt = cast (imgt, class (img));
endfunction
function acn = normalized_autocorrelation (psf)
idx = arrayfun (@colon, size (psf), repmat (-1, [1 ndims(psf)]),
repmat (1, [1 ndims(psf)]), "UniformOutput", false);
ac = convn (psf, conj (psf(idx{:})));
acn = ac / max (ac(:));
endfunction
%!assert (class (edgetaper (rand (100), rand (16))), "double")
%!assert (class (edgetaper (randi (255, 100, "uint8"), rand (16))), "uint8")
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