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Implementing International Standards On Still-Frame Image Compression Systems

This paper presents the results of the research that was conducted by Telephoto Communications into the effects of implementing the proposed ISO International Still-Frame Image Compression Standards. The objective of the research being to provide a commercial product which will comply with these standards. After providing a brief system description of the ALICE Type-120 and the "ISO compatible" product, the paper then reviews the modifications to the ALICE Type-120 algorithm to make it compatible with the proposed ISO standards and the performance impacts of these modifications. The primary elements of the ISO compatible system include: 1) Fast Discrete Cosine Transform (FDCT) 2) Differential Pulse Code Modulation (DPCM) of DC coefficients 3) Visual Quantization 4) Huffman encoding DPCM is a previous pel (pixel) predictor algorithm for coding DC coefficients. Visual quantization is a non-uniform quantization matrix based on the spectral position of each AC coefficient and takes advantage of the reduced sensitivity to high frequencies of the human visual system. Modifications to the ALICE Type-120 included the addition of the visual quantization and DPCM of the DC. The addition of these elements resulted in significantly improved compression ratios while maintaining a subjectively constant image quality. The research was conducted with the standard test images used in ISO evaluations and with special images used in the development of the ALICE Type-120 Image Compression System.