pad matrix to a particular size

Question

Elysi Cochin 2021-5-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/829368-pad-matrix-to-a-particular-size

评论： Hamza Mehmood 2022-8-27

采纳的回答： Image Analyst

在 MATLAB Online 中打开

I have a matrix M of size m x n

m and n may or may not be equal - M can be rectangular or square matrix - where m and n are less than 150,

I wanted to resize M to 150 x 150 by padding border with zeros, such that the m x n will come in the center

M_resized = padarray(M,[x y],0,'both');

how to compute value for x and y such that i can use the same line of code for any matrix,

or is there any another way to do?

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Answer 1

Image Analyst 2021-5-13

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https://ww2.mathworks.cn/matlabcentral/answers/829368-pad-matrix-to-a-particular-size#answer_699318

在 MATLAB Online 中打开

You can use the 'pre' and 'post' options to pad each side with the desired number of zeros.

Or use this "trick"

g = ones(150, 150); % Original matrix is 150 x 150
[rows, columns] = size(g);
m = 153
n = 152;
rowsPre = floor((m - rows)/2)
collsPre = floor((n - columns)/2)
% Pad it out with 334 rows top and bottom,
% and 281 columns left and right.
P = padarray(g, [rowsPre, collsPre], 0, 'both');
whos P  % Originally 152x152 padded with zeros all around.
% Not the size we want yet.  We want 153x152
% Here comes the "trick" to expand out the lower right corner with zeros.
P(m, n) = 0;
whos P  % Now 153 x 152

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Hamza Mehmood 2022-8-27

I have a similar problem.

I am trying to apply ssim index between a 25x25x25 Nifti and a 256x256x299 Nifti. Nifti is a 3D image.

For some context, I am trying to see whether infromation within a 25x25x25 ROI, extracted from a PET body scan of dimensions 256x256x299, is being activated within intermediate filter activations of 256x256x299. These intermediate filter activations were extracted from a pre trained 3D CNN model. No filter activation will result in a zero ssim value.

The ssim function cannot be applied between matrix of different dimensions so I decided instead to pad the 25x25x25 image with zeros and get it to the same dimension.

I was succesful in converting the 25x25x25 into 255x255x299 which is almost the same dimension. I then used the above trick to get the 255 to 256 and I was able to achive 256x255x299. No matter what I tried, that middle 255 did not turn 256.

I suspect the problem here lies in the last line of the code.

% Here comes the "trick" to expand out the lower right corner with zeros.

P(m, n) = 0;

I want the 25x25x25 to be padded to 256x256x299. How do I do it and what adjustments need to be made.

Many thanks !