Suprathreshold wavelet coefficient quantization in complex stimuli: psychophysical evaluation and analysis

A psychophysical experiment is described that quantifies human sensitivitie s to suprathreshold distortions caused by wavelet coefficient quantization in natural images, and the resulting analysis is explained. The quantizer s tep sizes that cause the first three visible degradations relative to the o riginal image are well predicted by exponential functions of subband standa rd deviation. The resulting root-mean-square (RMS) error in the image is co nstant for a spatial frequency and is independent of orientation. Contrast sensitivity calculations suggest a higher sensitivity to bands with higher energy, and threshold elevations for the second and third visible degradati ons are predicted well by the constant-RMS model. A quantization strategy b ased on the results is proposed for low-bit-rate applications. (C) 2001 Opt ical Society of America.