This is just a set of 6 small numbers - not a complete image where every pixel has an intensity value.
data = readmatrix('ab.txt')
x = data(:, 1);
y = data(:, 2);
plot(x, y, 'b.-', 'LineWidth', 2, 'MarkerSize', 40)
grid on;
Exactly how would you like to make those 6 (x,y) coordinates into an image? Would you like to use poly2mask, or perhaps exportgraphics???