Near computation-free compression of Fresnel holograms based on adaptive delta modulation

Abstract

Delta modulation (DM) is a classical technique that is generally applied to compress audio signals with a negligible amount of computation. Recently, it has been demonstrated that a similar approach can be applied to provide a moderate degree of compression, and at the same time maintain favorable coding fidelity, in compressing digital Fresnel holograms. The downside of this method is that it is necessary to determine an optimal step size for each of the source holograms through a trial and error process. In this paper we attempt to overcome this problem with adaptive delta modulation (ADM). Being different from the classical DM, the step size in ADM is automatically adjusted according to the intensity variation of the hologram. Experimental evaluation reveals that our proposed method is capable of attaining a compression ratio of 32 times without the need of determining the step size for each hologram. Hence, the proposed technique is useful for any holographic video system where holograms are needed to refresh at video rate. In addition, the proposed technique maintains favorable fidelity on the reconstructed images, and the complexity of both the encoding and decoding process is so small that they can be regarded as near computation-free operations.