Fast mode dependent directional transform via butterfly-style transform and integer lifting steps

Mode dependent directional transform (MDDT) can improve the coding efficiency of H.264/AVC but it also brings high computation complexity. In this paper we present a new design for implementing fast MDDT transform through integer lifting steps. We first approximate the optimal MDDT by a proper transform matrix that can be implemented with butterfly-style operation. We further factorize the butterfly-style transform into a series of integer lifting steps to eliminate the need of multiplications. Experimental results show that the proposed fast MDDT can significantly reduce the computation complexity while introducing negligible loss in the coding efficiency. Due to the merit of integer lifting steps, the proposed fast MDDT is reversible and can be implemented on hardware very easily.

Research highlights
► We first approximate the optimal MDDT by a proper trans- form matrix that can be implemented with butterfly-style operation.
► We further factorize the butterfly style transform into a series of integer lifting steps to eliminate the need of multiplications.
► Experimental results show that the proposed fast MDDT can significantly reduce the computation complexity while introducing negligible loss in the coding efficiency.