Perceptual optimization of image coding algorithms

We show how a model of the human visual system (HVS) can be used for encoder based perceptual optimization of JPEG. The HVS model takes into account the effects of light sensitivity, frequency sensitivity, and masking effects and is based on a hierarchy of oriented band pass filters. The model can be used to calculate a local frequency sensitivity, which in turn can be used to calculate perceptual weighting factors for each DCT coefficient in every block in the image. The proposed method is not limited to DCT based coders but is applicable to other coding schemes as well. The weighting factors can be used for adaptive quantization matrix design and for adaptive thresholding. We introduce a refinement of the adaptive thresholding technique that we call soft thresholding.