x = zeros(640, 480, 3);
x(:, 1:2:end, :) = 1;
This looks confusing to me in the online version: Where are the steps on the diagonal come from? They appear in a 64x48 pixels image also.
Locally in a figure of Matlab R2018b it looks, like image() is using a "nearest neighbor" interpolation:
All pixels are black or white.