Visual embedding of wavelet transform coefficients
Donald M. Monro, J.-L. Aufranc, M.A. Bowers, W. Poh · 2002
In wavelet image compression using embedded quantization, visual quality can be improved by limiting the number of bits used to refine each significant coefficient to some maximum which is different for each sub-band. At a fixed bit rate, the bits saved are used to augment the number of coefficients coded. In this work, a refinement strategy for just noticeable degradation is obtained experimentally for a 5-scale wavelet decomposition, giving a specification for visually lossless quantization. For a range of higher compression ratios, psychovisual experimentation to determine viewer preferences produces a scheme for the allocation of refinement bits at low bit rates. The results are consistent between subjects and across a range of standard test images. The work is a step towards wavelet image coding in which the data stream is fully embedded for optimum visual quality.