Image coding with windowed modulated filter banks
Lapped orthogonal transforms (LOT) have been introduced to provide a solution to the problem of blocking that occurs with transform coding at low bit rate. For the purpose of image coding, a more general class of exact reconstruction filter banks, that provides an additional degree of freedom in controlling ringing while relaxing the symmetry constraints of LOTs, is introduced. It is shown that windowed modulated filter banks are a very attractive candidate for image coding, since by allowing almost arbitrary selection of the window, they provide a control of the impulse response of the filters in the filter bank. The outputs of the windowed, modulated filter bank are quantized and entropy-coded in a way analogous to DCT (discrete cosine transform) coefficients. Comparisons are made between the filter bank and the DCT from the point of view of mean square error and subjective quality.<<ETX>>