An improved method is disclosed for the encoding phase for Wavelet-based compression
of digital data representing an object or image. Subband decomposition transforms
the data into hierarchical tree data. Two terms are precomputed: the highest bit-plane
in which any descendant of a node v has a non-zero bit (B1(v) and the
highest bit-plane in which any indirect descendant (grandchild and beyond) becomes
significant (B2(v). Node traversal is initiated but its extent is limited
by a fixed bit-budget. The number of bits emitted by a node as a function of the
bit-plane are counted through to the last bit-plane which exhausts the bit-budget.
The user can predetermine the coefficient, bit-plane and specific bit at which
the algorithm will halt. The tree structure is read only once, thus greatly accelereating
the encoding and reducing the memory reference rate by a factor of 2 or more. Accumulators
for each of the stacked bit-planes are provided which are incremented as each said
Wavelet coefficient is produced, by the number of bits that the coefficient adds
to the relevant bit-plane.
