how to recombine 4x4 nonoverlapping blocks into original matrix

the program for dividing the matrix is

clc;
close all;
clear all;
I=imread('C:\Users\user\Pictures\lenna.jpg');
I=rgb2gray(I);
A=imresize(I,[128,128]);
% disp(A);
% imshow(A);
[r c]=size(A);
b=4; 
k=0;
for i=1:(r/b)
for j=1:(c/b)
Block(:,:,k+j)=A((b*(i-1)+1:b*(i-1)+b),(b*(j-1)+1:b*(j-1)+b));
end
size(Block(:,:,k+j))
k=k+(r/b);
end

pls send the code to recombine these 4x4matrix