Finding the sparsest solution $\alpha$ for an under-determined linear system
of equations $D\alpha=s$ is of interest in many applications. This problem is
known to be NP-hard. Recent work studied conditions on the support size of
$\alpha$ that allow its recovery using L1-minimization, via the Basis Pursuit
algorithm. These conditions are often relying on a scalar property of $D$
called the mutual-coherence. In this work we introduce an alternative set of
features of an arbitrarily given $D$, called the "capacity sets".
We propose a direct reconstruction algorithm for Computed Tomography, based
on a local fusion of a few preliminary image estimates by means of a non-linear
fusion rule. One such rule is based on a signal denoising technique which is
spatially adaptive to the unknown local smoothness. Another, more powerful
fusion rule, is based on a neural network trained off-line with a high-quality
training set of images. Two types of linear reconstruction algorithms for the
preliminary images are employed for two different reconstruction tasks.