  By general relativistic magnetohydrodynamic simulations, it is suggested that
the rotational energy of a rapidly rotating black hole (BH) is preferentially
extracted along the magnetic field lines threading the event horizon in the
middle and lower latitudes. Applying this angle-dependent Poynting flux to the
jet downstream, we demonstrate that the jets exhibit limb-brightened structures
at various viewing angles, as observed from Mrk 501, M87, and Cyg A between 5
and 75 degrees, and that the limb-brightening is enhanced when the jet is
collimated strongly. It is also found that the jet width perpendicular to the
propagation direction shrinks at the projected distance of the altitude where
the jet collimates from a conical shape (near the BH) to a parabolic one (in
the jet). Comparing with the VLBI observations, we show this collimation takes
place within the de-projected altitude of 100 Schwarzschild radii from the BH
in the case of the M87 jet.
