1. A method for processing images obtained by tomography or tomosynthesis, the method comprising: acquiring a plurality of 2D projection images of an object using an imaging system, the acquiring a plurality of 2D projection images of an object being defined by Rf=s, wherein s is a vector of the acquired projections, R is a projection operator which models the imaging system and f is a 3D image of the object to be reconstructed with knowledge of R and s; processing the acquired 2D projection images including applying an iterative algorithm defined by its iteration, generating at least one set of processed projection images, the iteration being defined so that at each iteration the 3D image of the object is a linear function of the processed 2D projection images according to the property f (n) = R p (n) , wherein R is a matrix such that R Rf is a 3D image, wherein at each iteration, the algorithm generates a set of processed projection images, the iteration being defined for any vector in space of the 2D projection images by: 
 V[p ]=( I−ρR R ) p+ρs, wherein p (0) =ρs or p (0) =0, s is the set of acquired 2D projection images, ρ is a fixed parameter so that ∥1−ρ R R∥<1 and thereby guarantees convergence of the method, and I is the square unit matrix.