Lapped orthogonal transforms designed for error-resilient image coding
This paper describes a new design method for lapped orthogonal transforms (LOTs) that can provide a desired tradeoff between coding efficiency and resilience to transmission errors. Traditionally, LOT bases have been designed solely to maximize coding efficiency. When certain coefficients are lost due to transmission channel impairments, the reconstructed image is often unsatisfactory. Previously, we have developed a maximally smooth recovery method for image reconstruction from incomplete LOT coefficients (see Chung and Wang, ibid., vol.9, p.895-908, 1999). The reconstruction quality depends on the LOT basis used. We describe a new LOT-basis design method, which maximizes the weighted average of a coding gain and a reconstruction gain, with the latter being defined according to the maximally smooth recovery method. A coder using the designed basis with a high weighting factor toward the reconstruction gain can achieve significantly better reconstruction quality than a LOT basis that is designed to optimize the coding efficiency only. The newly designed bases are evaluated by their redundancy-rate-distortion performance. Simulation results show that the new bases are more efficient than the bases designed previously by S.S. Hemami (see ibid., vol.6, p.168-81, 1996), in that the new bases require fewer redundancy bits to achieve the same reconstruction quality under the same channel error pattern.