Sparsity and `something else'.

link: http://arxiv.org/abs/0909.2017
Abstract

The property of sparse representations concerning capability for information
storage is discussed. It is shown that this feature can be used, for instance,
for an application that we term Image Folding. The proposed procedure is
applicable by means of any suitable transformation. However, it is also the aim
of this paper to draw attention in regard to the gain in the sparsity of an
image representation achieved by combination of Discrete Cosine a Dirac
dictionaries.