2D Convolution algorithm error vs conv2 function

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billy papas
billy papas 2016-4-11
编辑： Andrei Bobrov 2016-4-11
[r,c] = size(x);
[m,n] = size(y);
h = rot90(y, 2);
center = floor((size(h)+1)/2);
Rep = zeros(r + m*2-2, c + n*2-2);
return
for x1 = m : m+r-1
for y1 = n : n+r-1
Rep(x1,y1) = x(x1-m+1, y1-n+1);
end
end
B = zeros(r+m-1,n+c-1);
for x1 = 1 : r+m-1
for y1 = 1 : n+c-1
for i = 1 : m
for j = 1 : n
B(x1, y1) = B(x1, y1) + (Rep(x1+i-1, y1+j-1) * h(i, j));
end
end
end
end
Con=conv2(Rep,h);
In this code ,after getting result of conv2 , i see that the above algorithm misses many elements of wanted output of convolution.Can someone help to fix this problem?

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回答（1 个）

Andrei Bobrov
Andrei Bobrov 2016-4-11
编辑：Andrei Bobrov 2016-4-11
a =reshape(1:12,4,[]);
b = reshape(1:8,2,[]);
without conv2
[m,n] = size(a);
[m1,n1] = size(b);
mn = [m,n] + 2*([m1,n1]-1);
a0 = zeros(mn);
a0(m1:(end-m1+1),n1:(end-n1+1)) = a;
i0 = reshape(1:numel(a0),mn(1),[]);
ii = i0(1:end-m1+1,1:end-n1+1);
i1 = bsxfun(@plus,(0:m1-1)',(0:n1-1)*mn(1));
idx = bsxfun(@plus,ii(:),i1(:)');
out = reshape(a0(idx)*reshape(rot90(b,2),[],1),m1+m -1,[]);
without conv2, with for loops
[m,n] = size(a);
[m1,n1] = size(b);
mn = [m,n] + 2*([m1,n1]-1);
a0 = zeros(mn);
a0(m1:(end-m1+1),n1:(end-n1+1)) = a;
b1 = rot90(b,2);
b2 = b1(:);
out = zeros(m1+m-1,n+n1-1);
for ii = 1:mn(1)-m1+1
for jj = 1:mn(2)-n1+1
x = a0(ii:ii+m1-1,jj:jj+n1-1);
out(ii,jj) = x(:)'*b2;
end
end
with conv2
out = conv2(a,b)
  1 个评论
billy papas
billy papas 2016-4-11
Thanks for the answer.But would like to optimize my code so that i can work.Your code seems really complex for my knowledge,although it's excellent as implementation.

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