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% RES = RCONV2(MTX1, MTX2, CTR)
%
% Convolution of two matrices, with boundaries handled via reflection
% about the edge pixels. Result will be of size of LARGER matrix.
%
% The origin of the smaller matrix is assumed to be its center.
% For even dimensions, the origin is determined by the CTR (optional)
% argument:
% CTR origin
% 0 DIM/2 (default)
% 1 (DIM/2)+1
% Eero Simoncelli, 6/96.
function c = rconv2(a,b,ctr)
if (exist('ctr') ~= 1)
ctr = 0;
end
if (( size(a,1) >= size(b,1) ) & ( size(a,2) >= size(b,2) ))
large = a; small = b;
elseif (( size(a,1) <= size(b,1) ) & ( size(a,2) <= size(b,2) ))
large = b; small = a;
else
error('one arg must be larger than the other in both dimensions!');
end
ly = size(large,1);
lx = size(large,2);
sy = size(small,1);
sx = size(small,2);
%% These values are one less than the index of the small mtx that falls on
%% the border pixel of the large matrix when computing the first
%% convolution response sample:
sy2 = floor((sy+ctr-1)/2);
sx2 = floor((sx+ctr-1)/2);
% pad with reflected copies
clarge = [
large(sy-sy2:-1:2,sx-sx2:-1:2), large(sy-sy2:-1:2,:), ...
large(sy-sy2:-1:2,lx-1:-1:lx-sx2); ...
large(:,sx-sx2:-1:2), large, large(:,lx-1:-1:lx-sx2); ...
large(ly-1:-1:ly-sy2,sx-sx2:-1:2), ...
large(ly-1:-1:ly-sy2,:), ...
large(ly-1:-1:ly-sy2,lx-1:-1:lx-sx2) ];
c = conv2(clarge,small,'valid');