  Histograms are among the most popular methods used in exploratory analysis to
summarize univariate distributions. In particular, irregular histograms are
good non-parametric density estimators that require very few parameters: the
number of bins with their lengths and frequencies. Many approaches have been
proposed in the literature to infer these parameters, either assuming
hypotheses about the underlying data distributions or exploiting a model
selection approach. In this paper, we focus on the G-Enum histogram method,
which exploits the Minimum Description Length (MDL) principle to build
histograms without any user parameter and achieves state-of-the art performance
w.r.t accuracy; parsimony and computation time. We investigate on the limits of
this method in the case of outliers or heavy-tailed distributions. We suggest a
two-level heuristic to deal with such cases. The first level exploits a
logarithmic transformation of the data to split the data set into a list of
data subsets with a controlled range of values. The second level builds a
sub-histogram for each data subset and aggregates them to obtain a complete
histogram. Extensive experiments show the benefits of the approach.
