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Abstract

A method of JPEG compression of an image frame divided up into a plurality of non-overlapping, tiled 8.times.8 pixel blocks B.sub.ij where i, j are integers covering all of the blocks in the image frame. A global quantization matrix Q is determined by either selecting a standard JPEG quantization table or selecting a quantization table such that the magnitude of each quantization matrix coefficient, Q.sub.ij is inversely proportional to a visual importance, I.sub.ij, to the image of a corresponding DCT basis vector. Next a linear scaling factor S.sub.ij is selected which defines bounds over which the image is to be variably quantized. Transform coefficients, D.sub.ijmn, obtained from a digital cosine transform of B.sub.ij, are quantized and the quantized coefficients T.sub.ijmn and Q*S.sub.min are entropy encoded, where S.sub.min is a user selected minimum scaling factor, to create a JPEG image file. The algorithm is unique in that it allows for the effect of variable-quantization to be achieved while still producing a fully compliant JPEG file.

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First Claim