Trying to stack an image array, error "Unable to perform assignment because the size of the left side is 220-by-220 and the size of the right side is 256-by-256"

I recieved a code in a matlab file that went as follows:

input_dir = './data/';

imgs = dir([input_dir '*.png']);

for i = 1:length(imgs)

temp = imread([input_dir imgs(i).name]);

stack(:,:,i) = double(temp);

end

I get this error: "Index in position 3 exceeds array bounds. Index must not exceed 1."

I tried to simplify the code to see if I could limit the issues I had:

image_unknown = imread('.\Images\Greyscale\data_0001.png');

for i = 1:length(image_unknown)

stack(:,:,i) = double(image_unknown);

end

I got this error: "Unable to perform assignment because the size of the left side is 220-by-220 and the size of the right side is 256-by-256".

The image is 256X256 pixels, but I have no idea why it says 220X220. I tried reading about what the stack function does, but it wasn't clear to me. Could someone explain what is happening here?

Answer 1

[KSSV]

If you RHS image is 3D and if the dimensions of each image are different, then you cannot save them into a matrix. So save them into a cell as shown below.

input_dir = './data/';
imgs = dir([input_dir '*.png']);
N = length(imgs) ; 
stack = cell(N,1) ; 
for i = 1:length(imgs)
    temp = imread([input_dir imgs(i).name]);
   stack{i} = double(temp);
end

You can access the cell array using stack{1}. stack{2}...stack{n}.

[David Raveh]

I was hoping I could get an explanation for what stack(:,:,i) means. Later in my code, I run this:

stack = stack(:,:,id_1:id_2);

where id_1 = 1 and id_2 = 99. I get this error.

Index in position 3 exceeds array bounds. Index must not exceed 1.

Error in registration_main (line 43)

stack = stack(:,:,id_1:id_2);

Could you explain what exactly I am doing when I run the code? Thanks.

[KSSV]

That means you are trying to extract the elements which are not present in the array. So it seems, your stack is only a 2D matrix, not a 3D matrix.

EXample:

A = rand(2,2,5) ;  % a 2x2x5 matrix for demo 
A(:,:,1:2) ; % no error
A(:,:,2:6) ; % error as there is no 6th matrix, it has only 5 2D arrays

Index in position 3 exceeds array bounds. Index must not exceed 5.