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% RES = ZCONV2(MTX1, MTX2, CTR)
%
% Convolution of two matrices, with boundaries handled as if the larger mtx
% lies in a sea of zeros. Result will be of size of LARGER vector.
%
% 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 (behaves like conv2(mtx1,mtx2,'same'))
% Eero Simoncelli, 2/97.
function c = zconv2(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 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);
clarge = conv2(large,small);
c = clarge(sy2:ly+sy2-1, sx2:lx+sx2-1);