1. A method of digital image modeling, a digital image divided into a plurality of digital image blocks, comprising the steps of: receiving a coder input vector of a plurality of digital image blocks; approximating a coefficient vector, each coefficient of the coefficient vector corresponding to one of the digital image blocks; wherein the step of approximating the coefficient vector comprises: generating a forward transformation matrix that yields a coefficient vector from a product of the coder input vector; and decomposing the forward transformation matrix into a product of at least one of a multi-diagonal transformation matrix and a sparse unitary transformation matrix and an energy sequencer unitary transformation matrix.