All-pass filtering is used to reduce the visual impact of erased subband trees. The image quality degrades gracefully with the erasure rate. The paper describes a simple subband coding method for combating packet erasures. No explicit redundancy coding is used, and provided the erasure rate is not too large, the visual impairment due to erasures is minor. The inverse all-pass filtering, at the decoder, has the "spread spectrum" effect of spreading over the whole image the spatially localised errors due to channel erasures. Since the filtering is unitary, the mean-squared error distortion is unchanged; however, the perceptual effect can be dramatic.
['Thomas R. Fischer', 'Qing Chen']
Subband image coding for packet erasure channels