Perceptual embedded image coding using wavelet transforms

We present a modified version of an embedded wavelet coding scheme, first suggested by Shapiro (see IEEE Transactions on Signal Processing, vol.41, no. 12, p.3445-3462, 1993), that improves the performance of the original algorithm in a visual subjective distortion sense. We preserve the features of the original Shapiro's embedded coder. It is possible to choose a fixed target bit rate, as the information needed to represent an image coded at some rate always contains the needed information for the same image coded at lower rates. Therefore, the decoder can cease decoding the bit stream at any point, simulating an image coded at a lower rate corresponding to the truncated bit stream. We also introduce some perceptive improvements by adopting different (more regular) filters with respect to the original QMF pyramid filters proposed by Simoncelli, Hingorani et al. (1987) and used by Shapiro. These filters are synthesized using a "wavelet approach" instead of a "subband approach", and this leads to a better control on their regularity properties, jointly with better perceptual performance.