Coding system and method for lossless and lossy compression of still and motion images

摘要

The invention relates to a coding system for lossless and lossy compression of still and motion images with means of statistical context modeling for adaptive entropy coding of wavelet coefficients in different conditioning templates. Furthermore, it is directed to a method for lossless and lossy compression of still and motion image data by hierarchical decomposing of said image data into subbands by a revertible wavelet transform that generates wavelet coefficients and by using a conditioning template for statistical context modeling and adaptive entropy coding of said wavelet coefficients. The compression ratio is improved by one or more of the following steps:adapting the shape and/or orientation of said conditioning template to different subbands;converting a two-dimensional array of signed wavelet coefficients into an equivalent sequence of only two input symbols for adaptive binary entropy coding;using previously scanned bit planes in forming conditioning templates;reducing the number of possible conditioning states corresponding to all possible combinations of events in the conditioning templates by using least-squares estimates of magnitudes of wavelet coefficients;reducing the number of possible conditioning states corresponding to all possible combinations of events in the conditioning templates by first using least-squares estimates of magnitudes of wavelet conditions: and then by minimum-entropy quantization of said estimates:comparing the so-far-coded bits of the coefficient being presently coded with the so-far-coded bits of the neighbouring coefficients and parent coefficient of to characterise spacial texture patterns and using them to augment the conditioning states created by the quantization of said estimates;conditioning the sign of a wavelet coefficient on the signs of neighbouring coefficients of .recording for each subband the location of the most significant bit of the coefficient of maximum magnitude in the subband and including it as side information in the code stream.