Mg. Ramos et Ss. Hemami, Suprathreshold wavelet coefficient quantization in complex stimuli: psychophysical evaluation and analysis, J OPT SOC A, 18(10), 2001, pp. 2385-2397
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.