Make squares in image white

In Matlab, I have this checkbox image that I am doing some work with. Now, I need to make it so all the squares are white and the other part of the image is black after I have done the imread() function. Then, I need to reverse it so the squares are black and the other part is white. I have managed to make it all black with what I have at the moment, but I haven't managed to get the white squares so far. What command or functions do I need to use?

My Code so far:

A=imread('chkbox.gif');

image(A);

colormap(gray(128));

Answer 1

[Matt J]

imcomplement(A);