/usr/share/octave/site/m/vlfeat/toolbox/imop/vl_imdown.m is in octave-vlfeat 0.9.17+dfsg0-6+b1.
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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 | function J = vl_imdown(I, varargin)
% VL_IMDOWN Downsample an image by two
% J = VL_IMDOWN(I) downsamples the image I by half by discarding
% each other pixel.
%
% VL_IMDOWN() accepts the following options:
%
% Method:: Sample
% 'Sample' downsamples the image by discarding
% pixels. 'Average' instead averages groups of 2x2 pixels.
%
% See also: VL_IMUP(), 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).
opts.method = 'sample' ;
opts = vl_argparse(opts, varargin) ;
switch lower(opts.method)
case 'sample'
J = I(1:2:floor(end-.5),1:2:floor(end-.5),:) ;
case 'average'
Iclass = class(I);
I = double(I);
J = ...
I(1:2:end-1,1:2:end-1,:) + ...
I(2:2:end,1:2:end-1,:) + ...
I(1:2:end-1,2:2:end,:) + ...
I(2:2:end,2:2:end,:) ;
J = J / 4 ;
eval(sprintf('J=%s(J);', Iclass));
otherwise
error('Unknown downsampling method ''%s''.', method) ;
end
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