| 摘要 |
PURPOSE:To improve the efficiency of the compression of image data by determining gradation components by sorting each block of plural pieces of picture elements into two groups, then inverting the resolution components depending on the gradation variation between neighboring blocks. CONSTITUTION:A buffer memory 1 accumulates image data equal to one block line length, and an average gradation calculating circuit 2 obtains the average gradation from said data. A group sorting circuit 3 compares the average gradation and the picture element data of one block, sorts the picture element into two kinds of groups depending on their magnitude-relation, and result is written in a resolution component memory 6. A group average gradation calculating circuit 4 obtains the average gradation of the sorted groups, and the result is written in a gradation component memory 5. A gradation variation decision circuit 7 decides the gradation variation out of the average gradation of the neighboring blocks. In case the gradation variation is mild, the resolution component for two blocks is read out from the memory 6, and a resolution component inversion circuit 8 inverts the resolution component signals of a second block B2 from white to black and black to white.
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