| 摘要 |
PURPOSE:To attain the efficient compression of an image by executing the gradation information reducing processing and picture element density reducing processing of respective image element data based on mode data determined in accordance with capacity difference between respective picture element data. CONSTITUTION:Plural picture element data out of respective picture element data in an image data having a halftone are collected as a block, each block is sorted into plural modes in accordance with the capacity difference between respective picture element data in the block and the gradation information reducing processing and picture element density reducing processing of the picture element data in each block are executed in accordance with parameters specified by the modes. Namely, a gradation information reducing circuit 6 changes the degree of gradation reduction at every block while referring the mode data M0-M3 in a mode selecting file, reduces the gradation reducing level of block data Db by detecting that a block with small values 0-3 of the mode data is a part with moderate density change or increases the gradation reducing level by deciding that a block with large values 0-3 is a part with sharp density change.
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