Device Selective Quantization for Reversible Wavelets

Compression with Reversible Embedded Wavelets (CREW), introduced at DCC 95, consists of three major parts: a wavelet transform, an embedded context model, and a binary entropy coder. The wavelet transform is a special implementation of high quality wavelet which provides perfect reconstruction with finite precision coefficients. The context model describes the wavelet coefficients in a particular order with conditional probability estimates. Finally the FSM-coder, a binary entropy coder described in DCC 93 with functionality similar to the QM-coder, is used to generate the final codestream. While CREW allows quantization to be done while encoding as is typical of most compression systems, a more useful method is illustrated in the figure at the bottom of the page. First the image is compressed losslessly and markers are provided in the compressed bit stream. When a decompressed image is needed the device characteristics are sent to a “parser.” As suggested by the name, the parser simply selects the appropriate portions of the bitstream for transmission using the device characteristics-no pixel or coefficient-level computation or entropy coding/decoding is performed. The parser is capable of providing data to display an image on a monitor, for example, by selecting compressed coefficients with low spatial resolution. For a different request the parser might select compressed coefficients to allow lossless decompression of a region of interest (ROI). The parser can also just send the bits necessary to go from a preview image to a printer resolution image or a full size medical monitor image (perhaps with 16 bit deep pixels).