A method of JPEG compression of an image frame divided up into a plurality
of non-overlapping, tiled 8.times.8 pixel blocks X.sub.i. 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[m,n] is inversely
proportional to the aggregate visual importance in the image of the
corresponding DCT basis vector. Next a linear scaling factor S.sub.i is
selected for each block, bounded by user selected values S.sub.min and
S.sub.max. Transform coefficients, Y.sub.i, obtained from a digital
cosine transform of X.sub.i, are quantized with global table S.sub.min Q
while emulated the effects of quantization with local table S.sub.i Q and
the quantized coefficients T.sub.i[m,n] and global quantization table
S.sub.min Q are entropy encoded , where S.sub.min is a user selected
minimum scaling factor, to create a JPEG Part 1 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 Part 1 file.