<title>JPEG compliant encoder utilizing perceptually based quantization</title>

Abstract

The international JPEG (Joint Photographics Experts Group) standards for image compression deal with the compression of still images. It specifies the information contained in the compressed bit stream, and a decoder architecture that can reconstruct an image from the data in the bit stream. However, the exact implementation of the encoder is not standardized. The only requirement on the encoder is that it generate a compliant bit stream. This provides an opportunity to introduce new research results. The challenge in improving these standards based codecs is to generate a compliant bitstream that produces a perceptually equivalent image as the baseline system that has a higher compression ratio. This results in a lower encoded bit rate without perceptual loss in quality. The proposed encoder uses the perceptual model developed by Johnston and Safranek to determine, based on the input data, which coefficients are perceptually irrelevant. This information is used to remove (zero out) some coefficients before they are input to the quantizer block. This results in a larger percentage of zero codewords at the output of the quantizer which reduces the entropy of the resulting codewords.