How can I put margins in an image?

Question

I have a binary image of 18x18 pixels and I want to put margins around this image with the purpose of obtaining an image 20x20 pixels.

The image is binary and

Answer 1

A=ones(18,18);%// your actual image
[M,N] = size(A);
B = zeros(M+2,N+2);%// create matrix
B(2:end-1,2:end-1) = A; %// matrix with zero edge around.

This first gets the size of your image matrix, and creates a zero matrix with two additional columns and rows, after which you can set everything except the outer edges to the image matrix.

Example with a non-square matrix of size [4x6]:

B =

     0     0     0     0     0     0     0     0
     0     1     1     1     1     1     1     0
     0     1     1     1     1     1     1     0
     0     1     1     1     1     1     1     0
     0     1     1     1     1     1     1     0
     0     0     0     0     0     0     0     0