Coding gain and spatial localisation properties of discrete wavelet transform filters for image coding

The authors consider coding gain and spatial localisation properties of DWT filters for still image compression. Using a JPEG type quantisation and encoding method several images are compressed using a DWT implemented using various two-band subband filter sets. It is concluded that a relatively high coding gain (relative to a highly correlated source) is necessary, but not sufficient, for good image coding performance. Further, it is observed that low spatial width filters are desirable, particularly in regard to reduced ringing distortion. In terms of the trade-off between coding gain and spatial localisation, and in terms of actual coding performance, it is shown that biorthogonal filters can outperform orthogonal filters