MATLAB Answers

resizing an image not working.

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Yaps
Yaps on 21 Oct 2018
Commented: Yaps on 21 Oct 2018

Hello, I am trying to resize a color image by using alternate pixel values. What I am getting is a blue image with a few black dots.I changed it to gray but now I am getting a white image with black image with a few black dots. Can someone tell me how to do the color resize, what is wrong with my script please

Thank you

    %read image
a =imread('beach.jpg');
a= rgb2gray(a);
[rows,columns] = size(a);
i = 1, j =1;
c=zeros(rows/2,columns/2);
for x = 1:2:rows
  for y = 1:2:columns
    c(i,j) = a(x,y);
     j = j + 1;
  end
  i = i +1;
  j = 1;
end
imshow(c);

  2 Comments

madhan ravi
madhan ravi on 21 Oct 2018
upload your .jpg file to test , you didn't attach the file

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Accepted Answer

Guillaume
Guillaume on 21 Oct 2018
Edited: Guillaume on 21 Oct 2018
For a greyscale image, your code is correct (as long as the size of the image is even) although note that iterating over rows in the inner loop and columns in the outer one would be faster due to the way matlab stores matrices in memory.
For colour image, your code will only look at the red channel, since it works on 2D arrays whereas colour images are 3D.
Of course, the whole thing is a waste of time, the following one liner would do the same more simply:
resizedimage = originalimage(1:2:end, 1:2:end, :);
with the added bonus that it works both for colour and greyscale images and works for odd and even sized images.

  1 Comment

Yaps
Yaps on 21 Oct 2018
Thank you for your help. It is helping me to understand how matlab works.

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