b = [2 1 8 24;9 10 3 12;2 5 8 19;1 2 3 4];
out = rot90(spdiags(tril(triu(flipud(diff(flipud(spdiags(b,-2:2))))),2)));
other variant without spdiags
s = size(b);
c = ones(s + [0 s(1)-1]);
c1 = rot90(tril(triu(c),s(2)-1));
c1(c1>0) = b';
c2 = diff(c1');
c3 = c2(:,end-1:-1:2);
t = tril(triu(ones(size(c3))),s(2)-2);
c3 = rot90(c3);
out = zeros(s-1)';
out(:) = c3(rot90(t)>0);
out = -out';
