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Abstract

An image compression system using the setting of fixed bit rates for compressing an image wherein image blocks are sorted into classes in accordance with the activities of the blocks, the activities being obtained by dividing an original image by a predetermined unit. Individual scale factors are given for each block, so that coding is carried out by fixing the allocating amount of bits to blocks to be coded. The system is operated by a method which detects activities according to a visual characteristic for each predetermined block unit, classifies blocks into corresponding classes based on the detected activities, sets a quantization scale factor corresponding to a sorted class by the average activity of the activities, controls the quantization by determining a quantization stepsize according to a predetermined value of a quantization table and a quantization scale factor, determines the pertinence of bit number of the quantized coefficient with respect to an allocated bit number per block, and repeatedly adjusts the block bit number to be output to carry out entropy coding. Thus, the quality of an image can be stabilized.

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First Claim