Padding an array with some size, and the location

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med-sweng 2015-2-7

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评论： Image Analyst 2015-2-7

Say that we have an array, and I wanted to resize that array while keeping its content. Something I thought of is "padding". When I tried that, I noticed that the original content had different locations in the new array. How can I pad they array, while keeping the original array content in their same location?

Thanks.

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Answer 1

Star Strider 2015-2-7

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编辑：Star Strider 2015-2-7

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I am not certain what you want, but this may work:

A = randi(10, 5, 4);                    % Original Array
B = zeros(10);                          % Preallocate Larger Array
B(1:size(A,1), 1:size(A,2)) = A;        % Create Padded Array

EDIT — It creates ‘A’ in ‘B’ such that the addressing (element references) are the same in both ‘A’ and ‘B’ for the original matrix ‘A’.

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Answer 2

Image Analyst 2015-2-7

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What did you try? Did you try padarray() in the Image Processing Toolbox?

m = magic(3);
mPadded = padarray(m, [4, 3])

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med-sweng 2015-2-7

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Yes, I used padarray().

For instance, for:

a=[1 3; 4 3; 5 3]

When I typed:

padarray(a,[4 4])

I got the following!

       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     1     3     0     0     0     0
       0     0     0     0     4     3     0     0     0     0
       0     0     0     0     5     3     0     0     0     0
       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0     0

Image Analyst 2015-2-7

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OK, glad it worked for you. It took your array and padded around it with zeros just like it was designed to do.

If you want the matrix not to be padded on all sides, but to keep it in the upper left, you can just assign the last element. For example:

b=magic(3);
b(8,6) = 0
b =
   1     6     0     0     0
   5     7     0     0     0
   9     2     0     0     0
   0     0     0     0     0
   0     0     0     0     0
   0     0     0     0     0
   0     0     0     0     0
   0     0     0     0     0