10. An imaging system, comprise: an imaging device having an optical mask and being configured for capturing an image of a scene, wherein said optical mask is selected to optically decompose said image into a plurality of channels, each being characterized by a different depth-dependence of a spatial frequency response of said imaging device; a non-transitory computer readable medium storing an in-focus dictionary defined over a plurality of dictionary atoms, and an out-of-focus dictionary defined over a plurality of sets of dictionary atoms, each set corresponding to a different out-of-focus condition; and a digital image processor configured for accessing said computer readable medium, for computing and storing in a memory at least one sparse representation of said decomposed image over said dictionaries, for generating a processed image using said sparse representation, and for displaying said processed image on a display device, wherein said image is divided into a plurality of patches, and wherein said computing is performed by expressing each patch as a combination of atoms of a sub-dictionary of said out-of-focus dictionary.
11. A portable device, comprising the imaging system of claim 10 .