Quantifying visual distortion in low-rate wavelet-coded images
Sheila S. Hemami, M.G. Ramos · 2002
An experiment quantifying human sensitivity to supra-threshold compression artifacts in wavelet-compressed images allows a computation and comparison of mean-squared errors producing equivalent visual distortion, and demonstrates that common assumptions used in wavelet image compression do not necessarily hold for low-rate images. The resulting MSE in the image is constant for a spatial frequency and is independent of orientation. Because the quantizers are not operating in the granular region, however, equal MSE does not imply equal quantizer step sizes. Computed threshold elevations for the second and third visible degradations are predicted well by the constant MSE model. Supra-threshold distortions in complex stimuli do not therefore behave according to sub-threshold assumptions, which suggest that the quantizer step size should be constant for a spatial frequency.