Optimal PSNR estimated spectrum adaptive postfilter for DCT coded images
I. Linares · 2002
Our previous work aimed at reducing the blocking distortion of DCT coded images is further improved by introducing the optimal PSNR estimated spectrum adaptive postfilter (ESAP) algorithm. ESAP searches for a one dimensional log-sigmoid weighting function which, when applied to the separable, interpolated local block estimated spectrum of the coded image, minimizes the mean square error (MMSE) with respect to the original image using a 2-D steepest descent search. Convergence is obtained in a few iterations for integer parameters. A unique maximum PSNR is guaranteed given the asymptotic exponential overshoot behavior of the surface generated by ESAP. We obtained PSNR improvement of 1.5 dB over nonpostfiltered JPEG images as well as subjective improvement. ESAP is based on a DFT analysis of the DCT basis functions and uses spatially adaptive separable FIR postfilters.