  We present a family of easily computable upper bounds for the Holevo quantity
of ensemble of quantum states depending on a reference state as a free
parameter. These upper bounds are obtained by combining probabilistic and
metric characteristics of the ensemble. We show that appropriate choice of the
reference state gives tight upper bounds for the Holevo quantity which in many
cases improve existing estimates in the literature.
  We also present upper bound for the Holevo quantity of a generalized ensemble
of quantum states with finite average energy depending on metric divergence of
the ensemble. The specification of this upper bound for the multi-mode quantum
oscillator is tight for large energy.
  The above results are used to obtain tight upper bounds for the Holevo
capacity of finite-dimensional and infinite-dimensional energy-constrained
quantum channels depending on metric characteristics of the channel output.
