Compression with Reversible Embedded Wavelets (CREW) is a unified lossless and lossy continuous-tone still image compression system. It is wavelet-based using a "reversible" approximation of one of the best wavelet filters. Reversible wavelets are linear filters with non-linear rounding which implement exact-reconstruction systems with minimal precision integer arithmetic. Wavelet coefficients are encoded in a bit-significance embedded order, allowing lossy compression by simply truncating the compressed data. For coding of coefficients, CREW uses a method similar to Shapiro's zerotree, and a completely novel method called Horizon. Horizon coding is a context based coding that takes advant.age of the spatial and spectral information available in the wavelet domain. CREW provides state of the art lossless compression of medical images (greater than 8 bits deep), and lossy and lossless compression of 8-bit deep images with a single system. CREW has reasonable software and hardware implement at ions.
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