Parallel FIR filter banks for robust subband image coding

Novel filter banks for low-bit-rate image subband coding are presented. To avoid extensive ringing noise, the unit pulse responses of the synthesis channels are kept short. This calls for special measures to avoid blocking effects. The synthesis lowpass unit pulse response must be a good interpolator if blocking effects are to be avoided. Earlier work has shown that nonunitary filter banks can offer superior coding gain compared with unitary filter banks. This result is extended by indicating that the analysis and synthesis parts have different tasks to perform. The analysis filter banks should pack the data energy, while the synthesis filter banks should provide blocking-free reconstruction with negligible ringing artifacts in the presence of noise. Using these basic ideas, nonunitary filter banks are designed which have superior properties compared with the DCT (discrete cosine transform) and the LOT (lapped orthogonal transform), in terms of coding gain and blocking effects.<>