  Blackbody radiation, emitted from a furnace and described by a Planck
spectrum, contains (on average) an entropy of $3.9\pm 2.5$ bits per photon.
Since normal physical burning is a unitary process, this amount of entropy is
compensated by the same amount of "hidden information" in correlations between
the photons. The importance of this result lies in the posterior extension of
this argument to the Hawking radiation from black holes, demonstrating that the
assumption of unitarity leads to a perfectly reasonable entropy/information
budget for the evaporation process. In order to carry out this calculation we
adopt a variant of the "average subsystem" approach, but consider a tripartite
pure system that includes the influence of the rest of the universe, and which
allows "young" black holes to still have a non-zero entropy; which we identify
with the standard Bekenstein entropy.
