Differential video image compression in holographic media

Abstract

A video image F›k! is identified as a basis image and stored as a basis page S›k! in a holographic storage medium. A subsequent image F›k+n! is stored by recording in the medium a page S›k+n!=F›k+n!-a›k!F›k!, where a›k!.noteq.0 and preferably a›k!=1. The page S›k! is recorded with a reference beam R›k!, while S›k+n! is recorded with a reference beam R›k+n! orthogonal to R›k!. The basis page is reset whenever the average intensity of a page to be stored exceeds a predetermined threshold. An image F'›k! is retrieved by reading basis page S›k! and letting F'›k!=S›k!. Subsequent images F'›k+n! are retrieved as S›k+n!+b›k!S›k!, where b›k!.noteq.0 and preferably b›k!=a›k!=1. The page addition step is performed coherently, i.e. by accessing the medium with a reference wave function R›k+n!+b›k!R›k!. The coherent addition is achieved by using a compound phase-and-amplitude modulator in a phase-code-multiplexed system, and by simultaneously accessing the storage medium at two different angles in an angle-multiplexed system. Differential video compression leads to a reduction in interpage crosstalk and to a capacity increase in crosstalk-limited memories. Optical page-by-page addition allows fast readout and eliminates the need for a time-consuming electronic decompression step.

Dependencies are inferred from the claim text.