Duplicating the rows and columns of image, without using imresize.

I am trying to take an image and output a larger image whose height and width are twice as much as those of the input image, by duplicating the rows and columns ( without using imresize).

I have tried implementing this; however, the output is an entirely black image.

img = imread('https://people.sc.fsu.edu/~jburkardt/data/png/lena.png');
[M1,N1] = size(img);
M2 = M1*2;
N2 = N1*2;
g = zeros(M2,N2);
imshow(g);

[Rik]

Why do you not want to use imresize? Is this a homework assignment?

If you follow the flow of your program, the following things happen:

1. you read a color image from a website to an array
2. you determine the number of rows and columns (ignoring a possible color component, which is aparently missing from this version of the lena image)
3. you double those numbers
4. you create an entirely new array made up of only zeros
5. you display that new array

From this it should be clear that you didn't change the size of the image, and it should be clear why the image you see is blank.

Answer 1

[TADA]

The image is black because you are displaying zeros

You say that you want to duplicate the rows and columns - I assume you mean stretching each pixel to 4 identical pixels

That can be done using repelem if you don't care about the massive pixelation

img = imread('autumn.tif');
multFactor = 2;
stretchedImg = repelem(img, multFactor, multFactor);
imshow(stretchedImg);