Optical EngineeringHexagonal subband image coding with perceptual weighting
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A hexagonally sampled image is split into a low passband and nine passbands of one octave width and 60 deg angular orientation. The conditions to be satisfied by the filter banks for perlect reconstruction are presented. The human visual system's response to stimuli at differing spatial frequencies is then employed to shape the coding noise spectrum. Rate is allocated under a frequency-weighted mean-square-error distortion measure. A framework is presented employing either the power spectral density of the image or the variance of the subbands. Both adaptive and nonadaptive entropy coding simulations are carried out under a Laplacian source distribution. Transparent coding results are presented at rates below 1 bit/pixel.