Perceptual adaptive JPEG coding

An extension to the JPEG standard (ISO/IEC DIS 10918-3) allows spatial adaptive coding of still images. As with baseline JPEG coding, one quantization matrix applies to an entire image channel, but in addition the user may specify a multiplier for each 8/spl times/8 block, which multiplies the quantization matrix, yielding the new matrix for that block. MPEG 1 and 2 use much the same scheme, except there the multiplier changes only on macroblock boundaries. We propose a method for perceptual optimization of the set of multipliers. We compute the perceptual error for each block based upon the DCT quantization error adjusted according to the contrast sensitivity, light adaptation, and contrast masking, and pick the set of multipliers which yield maximally flat perceptual error over the blocks of the image. We investigate the bit rate savings due to this adaptive coding scheme and the relative importance of the different sorts of masking on adaptive coding.