Padding an image in MATLAB

Question

I have an image of size 61x56 and I want to pad the image to size 392x392.

I am trying to use padarray but since I get a non-integer value I am unable to do this. Can anyone help me with this. Thanks a lot! I have attached what I want to do below.

K = imread('test.jpg');
K = rgb2gray(K);
[m n] = size(K);
p = 392;
q = 392;
K_pad = padarray(K, [(p-m)/2 (q-n)/2], 'replicate');

Answer 1

You can divide your padarray instruction in two calls:

K_pad = padarray(K, [floor((p-m)/2) floor((q-n)/2)], 'replicate','post');
K_pad = padarray(K_pad, [ceil((p-m)/2) ceil((q-n)/2)], 'replicate','pre');

But you may want to check what is happening in the corners of the image to see if it is ok with what you want to do with it.

Answer 2

You can try this function:

function out1 = myresize(in1)
%% [e-mail]
%% resize an image to closest power of 2

[m,n] = size(in1);

if(rem(m,2)~=0)
    in1(1,:)=[];
end

if(rem(n,2)~=0)
    in1(:,1)=[];
end

[m,n] = size(in1);

a = max(m,n);

if(log2(a)~=nextpow2(a) || m~=n)

    s1 = 2^nextpow2(a);
    n_row = (s1 - m)/2;
    n_col = (s1 - n)/2;

    dimension = [n_row,n_col];

    out1 = padarray(in1,dimension);

end
end

for example:

A = ones(2,8);
out1 = myresize(A);

first it finds the maximum of rows and columns, then paddarray the matrix in both direction.

Answer 3

Here's another way of padding it without using padarray.

imgSize=size(img); %#img is your image matrix
finalSize=392;   
padImg=zeros(finalSize);

padImg(finalSize/2+(1:imgSize(1))-floor(imgSize(1)/2),...
    finalSize/2+(1:imgSize(2))-floor(imgSize(2)/2))=img;