Just look at it one bit at a time. The first time, you take an array of zeros and then set every other row and every other column element to 1.
n = 8;
a = zeros(n);
a(1:2:n,1:2:n) = 1;
Look at a, every other column and every other row are all zeros.
Look at a as an image:
imagesc(a);
Now the next line:
a(2:2:n,2:2:n) = 1;
Adds a one staring in the 2nd column and 2nd row. It then jumps every other column and the same with the rows (putting in a 1).
Now look at a with the bone colormap.
imagesc(a); colormap(bone)
