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');

score 6 · Accepted Answer · answered Jul 06 '11 at 13:45

6

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.

answered Jul 06 '11 at 13:45

Aabaz

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I wonder if it can be done more efficiently with only one memory copy. – Royi Aug 02 '14 at 00:57

score 6 · Answer 2 · edited Jul 03 '19 at 13:22

6

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;

edited Jul 03 '19 at 13:22

Adriaan

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answered Jul 06 '11 at 13:47

abcd

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Will it only pad with zeros? What if you wanted the `replicate` functionality? – Royi Aug 02 '14 at 00:56
@4Oh4 please do not edit the code of others. Instead, leave a comment with why you think it should be changed. The OP might have written this code with a specific purpose in mind, and should not be changed without their approval. – Adriaan Jul 03 '19 at 13:24

score 0 · Answer 3 · answered Jun 30 '17 at 01:40

You can try this function:

function out1 = myresize(in1)
%% Sa1habibi@gmail.com
%% 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.

Padding an image in MATLAB

3 Answers3

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