| 摘要 |
PROBLEM TO BE SOLVED: To provide an image compression apparatus capable of compression without damaging a density difference in an intermediate color region even when both the intermediate color region and a line drawing region with a large density difference are present in the same block. SOLUTION: A limited tone range (example; 64-192) narrower than a tone range (256 tones) that image data can take is set in a setting part 13, a maximum value/minimum value detection part 14 detects the maximum value and the minimum value within the limited tone range of a tone value in one block, a threshold generation part 15 divides the tone range having them at both ends into a plurality of regions, and a judgement part 16 judges whether or not the tone values of respective pixels are within the limited tone range. An encoding part 17 encodes the pixel whose tone value exceeds the upper end value of the limited tone range to a first code, the pixel whose tone value is less than the lower end value of the limited tone range to a second code, and the pixel within the limited tone range to the code corresponding to the region to which the tone value of the pixel belongs among the plurality of previously divided regions. COPYRIGHT: (C)2009,JPO&INPIT
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