Randomly samplying a matrix

Im currently modifying an algorithm which randomly samples a given matrix by

%   Omega - set of observed entries.  Should be linearly indexed.
%
%   A - data vector of the form M(Omega)
[m,n] = size(M);
I = randi([0 1],m,n);
Omega = find(I);
A = M(Omega);

I wonder is it possible to replace the omega by a mask image which is made of text intead of randomly generating it.

[KSSV]

Omega in the above line of codes is a inde, it should be logical/ double. How you can take a text?

[fadams18]

Thats the problem.

I tried to modify the algorithm by doing this:

 
Input_Image = double(imread('/home/Desktop/relatedworks/re1.jpg'));
mask = double(imread('/home/Desktop/relatedworks/block_text.bmp'));
mask = mask ./ max(mask(:));       % index matrix of the known elements
X = Input_Image.*mask;

The original code randomly removed entries of the randomly generated matrix M whereas im trying to mask an image with text. The text in this case serves as the missing entries of my image. is there a workaround this?

I tried to replace Omega by mask and A by X. I get this error when i run the algorith

Subscript indices must either be real positive integers or logicals.
Error in mc_nmf (line 65)
    Z = zeros(m,n);  Z(Omega) = A;