/usr/share/octave/site/m/vlfeat/toolbox/imop/vl_imgrad.m is in octave-vlfeat 0.9.17+dfsg0-6+b1.
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 | function [Fx,Fy] = vl_imgrad(F,varargin) ;
% VL_IMGRAD Image gradient
% [Fx,Fy] = VL_GRAD(F) returns the finite differencies gradient of the
% image F. The function uses central differencies and for all but
% the boundaries pixels, for which it uses forward/backward
% differencies as appropriate.
%
% VL_GRAD(F,'forward') uses only forward differencies (except on the
% lower and right boundaries, where backward difference is used).
% Similarly, VL_GRAD(F,'backward') uses only backward differencies.
%
% See also: GRADIENT(), VL_HELP().
% Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
% All rights reserved.
%
% This file is part of the VLFeat library and is made available under
% the terms of the BSD license (see the COPYING file).
type = 'central' ; % forward, backward
for k=1:2:length(varargin)
switch varargin{k}
case 'Type'
type = varargin{k+1} ;
otherwise
error(['Parameter ''', varargin{k}, ''' unknown']) ;
end
end
[M,N]=size( F ) ;
switch type
case 'central'
Fx = [ F(:,2)-F(:,1) , ...
0.5*(F(:,3:end)-F(:,1:end-2)) , F(:,end)-F(:,end-1) ] ;
Fy = [ F(2,:)-F(1,:) ; ...
0.5*(F(3:end,:)-F(1:end-2,:)) ; F(end,:)-F(end-1,:) ] ;
case 'forward'
Fx = [ F(:,2:end)-F(:,1:end-1) , F(:,end)-F(:,end-1) ] ;
Fy = [ F(2:end,:)-F(1:end-1,:) ; F(end,:)-F(end-1,:) ] ;
case 'backward'
Fx = [ F(:,2)-F(:,1) , F(:,2:end)-F(:,1:end-1)] ;
Fy = [ F(2,:)-F(1,:) ; F(2:end,:)-F(1:end-1,:)] ;
otherwise
error(['Difference type ''', type, ''' unknown']) ;
end
|