Sparse molecular image representation

• We design a new structured sparsity prior with emphasis on the code coefficients.
• We propose the idea of atom pools for describing the variability in the sparse codes.
• We differentiate between molecule prototypes and realizations to add flexibility.
• We design a new algorithm for sparse coding under our new structured sparsity prior.
• We provide experimental results in illustrative image restoration applications.

Sparsity-based models have proven to be very effective in most image processing applications. The notion of sparsity has recently been extended to structured sparsity models where not only the number of components but also their support is important. This paper goes one step further and proposes a new model where signals are composed of a small number of molecules, which are each linear combinations of a few elementary functions in a dictionary. Our model takes into account the energy on the signal components in addition to their support. We study our prior in detail and propose a novel algorithm for sparse coding that permits the appearance of signal dependent versions of the molecules. Our experiments prove the benefits of the new image model in various restoration tasks and confirm the effectiveness of priors that extend sparsity in flexible ways especially in case of inverse problems with low quality data.