function M = roirect()
    [x y] = ginput(2);
    s = size(currentImage);
    M(1:s(1),1:s(2)) = 0;
    x = fix(sort(x));
    y = fix(sort(y));
    M( y(1):y(2), x(1):x(2) ) = 1;
    M = logical(M);