CODEWITHSUNDEEP
imagematlabimage-processingresize
Ana Ain
Ana Ain

Reputation: 173

Re-sizing a rectangular image to a square image

I have an image, size 213 x 145 pixels. I want to resize it to 128 x 128 pixels for example. I've already tried the code below:

i = imread ('alif1.png');
I = imresize (i, [128 128], 'bilinear');

OR
i = imread ('alif1.png');
I = imresize (i, [128 128], 'lanczos3');

it gave me a square image, but the image became disproportionate. However, I believe the aspect ratio was preserved. I want to resize the image to a square shape without distorting or stretching the image, rather to pad/crop the white background instead. I still can't figure out the right code. I hope anyone could help.

Upvotes: 1

Views: 2120

Answers (2)

user2261062
user2261062

Reputation:

If you want to resize (not crop) the image and keep the aspect ratio (so you don't loose any part of the image AND it doesn't get distorted), you can first add margins to make the image squared.

You can achieve this using the function padarray, or just creating a new image of zeros and then adding your image in the appropiate coordinates.

Once your image is squared, you can resize it to 128x128 using imresize.

In order to add margins, you will have to see where to add them (top&bottom OR left&right). Also since padarray adds the same amount of margins in both sides, you have to check if the number you need is even. If it's odd add first a last row (or column) of zeros to your image.

So basically you have three options:

  • Make the image squared by not preserving aspect ratio (which is what you already tried)

  • Cropping the image as suggested by @ShvetChakra and @bla (but you will loose some image info)

  • Add margins to the image and resize (but you will end up with a squared image with margins)

    Magic doesn't exist so "you must choose, but choose wisely"

(Quote from Indiana Jones and the Last Crusade).

EDIT:

% Example with a 5x2 image, so an extra column will be added 
% in order to use padarray.
im = [1 2; 3 4; 5 6; 7 8; 9 10];

nrows = size(a,1);
ncols = size(a,2);

d = abs(ncols-nrows);    % difference between ncols and nrows:
if(mod(d,2) == 1)        % if difference is an odd number
    if (ncols > nrows)   % we add a row at the end
        im = [im; zeros(1, ncols)];
        nrows = nrows + 1;
    else                 % we add a col at the end
        im = [im zeros(nrows, 1)];
        ncols = ncols + 1;
    end
end

if ncols > nrows
    im = padarray(im, [(ncols-nrows)/2 0]);
else
    im = padarray(im, [0 (nrows-ncols)/2]);
end

% Here im is a 5x5 matix, not perfectly centered 
% because we added an odd number of columns: 3

Upvotes: 1

Shvet Chakra
Shvet Chakra

Reputation: 1043

I = imread('alifi.png');
Crop image, specifying crop rectangle.

I2 = imcrop(I,[75 68 128 128]);

Size and position of the crop rectangle, specified as a four-element position vector of the form [xmin ymin width height].

for more understanding follow this(matlab ) and this(blog) links.

Upvotes: 2

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