Apparatus and method for compressing information

In a digital compression decoder for reconstructing image data from a bit stream comprising data bits of arithmetic-coded symbols comprising a ZEROTREE symbol, an ISOLATED ZERO symbol, and at least one type of non-zero symbol that define coefficient models for an array of multibit coefficients of wavelet-transformed hierarchical decomposed subbands of said image data;

• wherein said decoder has an a priori knowledge of the protocol for the order in which the wavelet-transformed multibit coefficients of said array were scanned on compression so that a list of the coordinates of the multibit coefficients of the lowest low (LL) wavelet-transformed subband of said array are predetermined;
• wherein (a) a ZEROTREE symbol occurs at first given coordinates of of said LL subband or at coordinates of descendents of said first given coordinates of said LL subband which correspond to coefficients that are zerotree roots, (b) an ISOLATED ZERO symbol occurs at second given coordinates of of said LL subband or at coordinates of descendents of said second given coordinates of said LL subband which correspond to isolated-zero coefficients, and (c) at least one type of non-zero symbol at third given coordinates of said LL subband or at coordinates of descendents of said third given coordinates of said LL subband which correspond to non-zero coefficients;
• the improvement for efficiently reconstructing said image data wherein said decoder comprises:
• data decoding means responsive to said data bits applied thereto for deriving the data values of said wavelet-transformed multibit coefficients from said arithmetic-coded symbols that starts with a list of coordinates of said relatively small number of multibit coefficients of said LL subband of said array and a relatively high initial threshold value for dynamically deriving in sequence the values of said wavelet-transformed multibit coefficients first at said relatively high initial threshold value and then at one or more successively lower threshold values by ignoring from consideration in said sequential dynamic derivation all coordinates of coefficients which are descendents of coordinates which have already been found in said sequential dynamic derivation to be occupied by a ZEROTREE symbol.

A system comprising (1) an encoder for efficiently generating a digital compressed code in response to an array of a relatively large number of multibit coefficients defining image data at a relatively high resolution that has been hierarchical subband decomposed by a wavelet transform at a given plurality of lower resolutions, whereby the lowest low (LL) subband comprises an array having the smallest number of multibit coefficients of all the wavelet-transform subband arrays, each LL subband multibit coefficient comprises an ancestor of all multibit coefficients of all higher subbands descended from that LL subband multibit coefficient, and each of said multibit coefficients of said LL subband and said multibit coefficients of said descendents thereof includes a most significant bit;

• wherein said encoder includes coding means for deriving said data-compressed code comprising (a) a ZEROTREE symbol at first given coordinates of of said LL subband or at coordinates of descendents of said first given coordinates of said LL subband which are occupied by coefficients that are zerotree roots, (b) an ISOLATED ZERO symbol at second given coordinates of of said LL subband or at coordinates or descendents of said second given coordinates of said LL subband which are occupied by isolated-zero coefficients, and (c) at least one type of non-zero symbol at third given coordinates of of said LL subband or at coordinates of descendents of said third given coordinates of said LL subband which are occupied by non-zero coefficients;
• and (2) a decoder for efficiently decoding the digital compressed code generated by said encoder;
• wherein:
• said encoder includes (3) means responsive to each multibit coefficient of said LL subband and said multibit coefficients of all of its descendents of said wavelet transform for deriving a zerotree map, wherein said zerotree map includes a zerotree-map multibit coefficient corresponding to each coefficient of said LL subband array, and each zerotree map coefficient has a binary "1" value in a bit position thereof only if either its corresponding LL-subband-array coefficient itself or any of the descendents of its corresponding LL-subband-array coefficient has its most significant bit in that bit position, and (4) said coding means includes means that starts with a list of coordinates of said relatively small number of coefficients of said LL subband of said array and a relatively high initial threshold value for dynamically deriving in sequence said data-compressed code from the multibit coefficients of the wavelet-transform subband and the multibit coefficients of the zerotree map first at said relatively high initial threshold value and then at one or more successively lower threshold values by ignoring from consideration in said sequential dynamic derivation all coordinates of coefficients which are descendents of coordinates which have already been found in said sequential dynamic derivation to be occupied by coefficients that are zerotree roots;
• and
• said decoder includes (5) data decoding means responsive to said data bits of said arithmetic-coded symbols of said data-compressed bit stream applied thereto for deriving the data values of said wavelet-transformed multibit coefficients from said arithmetic-coded symbols that starts with a list of a priori known coordinates of said relatively small number of multibit coefficients of said LL subband of said array and a relatively high initial threshold value for dynamically deriving in sequence the values of said wavelet-transformed multibit coefficients first at said relatively high initial threshold value and then at one or more successively lower threshold values by ignoring from consideration in said sequential dynamic derivation all coordinates of coefficients which are descendents of coordinates which have already been found in said sequential dynamic derivation to be occupied by a ZEROTREE symbol.