1. block_divide

% 返回的块向量构成的矩阵，其维度信息为 K^2 * N，每一列由块构成的列向量
function P = block_divide(I, K)

    r = size(I, 1)/K;
    c = size(I, 2)/K;
    P = zeros(K^2, r*c);

    f = @(A) A(:);

    for i = 1:r,
        for j = 1:c,
            P(:, (i-1)*c+j) = f(I(K*(i-1)+1:K*i, K*(j-1)+1:K*j));
        end
    end 
end

2. re_divide

% col: 原始图像矩阵的行数
function I = re_divide(P, col, K)
    N = size(P, 2);
    m = floor(sqrt(N));
    b44s = [];
    for i = 1:N,
        b44s = [b44s, reshape(P(:, i), K, K)];
    end
    I = [];
    for k = 1:m,
        I = [I; b44s(:, (k-1)*col+1:k*col)];
    end
end