  On the kiloparsec scale, extragalactic radio jets show two distinct
morphologies related to their power: collimated high-power jets ending in a
bright termination shock and low-power jets opening up close to the core and
showing a more diffuse surface brightness distribution. The emergence of this
morphological dichotomy on the parsec scale at the innermost jet regions can be
studied with very-long-baseline interferometry (VLBI) radio observations of
blazars in which the jet emission is strongly Doppler boosted due to
relativistic bulk motion at small angles between the jet direction and the line
of sight. We seek to characterize the geometry and emission profiles of the
parsec-scale radio jets of flat-spectrum radio quasars (FSRQs) and BL Lacertae
objects (BL Lacs) on parsec scales to derive properties of the magnetic field,
environment, and energetics for different classes of extragalactic jets. We
analyze the VLBI radio data of 15 FSRQs, 11 BL Lacs, and two radio galaxies
contained in both the MOJAVE data archive and the Boston University BU blazar
group sample archive at 15 GHz and 43 GHz, repectively. We derived the
brightness-temperature and jet-width gradients along the jet axis from
parameterizations of the jets using 2D Gaussian brightness distributions. In
most BL Lac objects, the diameter and brightness-temperature gradients along
the jet axis can generally be described well by single power laws, while the
jets of FSRQs show more complex behavior and remain more strongly collimated on
larger physical scales. We find evidence for a transition of the global jet
geometry from a parabolic to a conical shape in the BL Lac objects 3C 66A, Mrk
421 and BL Lacertae, the radio galaxy 3C 111 and the FSRQs CTA 26, PKS
0528+134,4 C +71.07,4C +29.45, and 3C 279 outside the Bondi sphere.
