In an assignment a(:) = b, the number of elements in a and b must be the same

Question

Problem:

For the following code :

E = [5,200];  Selected edge values 
    X = imread('LENNA128.bmp');
    N = length(X);
    Y = false(N+2);
for k = 1:numel(E);
    Y(2:end-1,2:end-1) = X==E(k);
    Z = Y(1:end-2,2:end-1) | Y(3:end,2:end-1) | Y(2:end-1,3:end) | Y(2:end-1,1:end-2);
    X(Z) = round((X(end-3,3:end-2) + X(end-3,4:end-1))/2);
end

I get the error message:

In an assignment  A(:) = B, the number of elements in A and B must be the same

Can anyone help me out to solve this problem.

Answer 1

The problem with you code is explained below:

Problem 1: The use of length with a 2D matrix
If your image is not square, N will be the size of the largest dimension of your image. Y will always be a square image two pixels larger in both dimensions than the largest dimension of your image. The assignment
   Y(2:end-1,2:end-1) = X==E(k)
will then fail as you're trying to assign a non-square matrix to a square matrix.
The simplest way to fix this is to declare:
N = size(X); %%assuming that |X| is a greyscale or indexed image.
Problem 2: Most likely the one that causes the error message:
X(Z) = round((X(end-3,3:end-2) + X(end-3,4:end-1))/2)

Z is a logical array which will select as many element of X as there are true values in Z. The other side of the assignment is the moving average of one the last row of the image excluding the first two pixels. It is a row vector with 2 less elements than the number of columns of X. I don't see why this would have as many values as there are true values in Z.

Hope you understand the problems and can solve it now.

Happy coding.