function z = symconvup(x,f1,f2,fln,keep)
y = zero([2 1].*size(x));       y(1:2:end,:) = x;
y = conv2(y,f1');
z = zeros([1 2].*size(y));      z(:,1:2:end) = y;
z = conv2(z,f2);
z = z(fln - 1:fln + keep(1) - 2, fln - 1:fln + keep(2) -2);