Reversible factorization of half-sample symmetric (HS) filter banks (filters with even-length impulse responses) is proving problematic. In contrast to the WS case, reversibility for HS filter banks is highly dependent on the choice of rounding rule(s) used to achieve reversibility. This issue is intimately tied to the HS boundary-handling technique (i.e., (2,2)-symmetric pre-extension). Consequently, the USNB is recommending that boundary extension policy for HS filter banks be defined in terms of interleaved lifting extensions rather than symmetric pre-extension.

LA-UR-01-1516 Presented at 23rd Meeting of ISO/IEC JTC 1/SC 29/WG 1, JPEG in Singapore