| 摘要 |
PURPOSE:To reduce a loss in the gradation information of an original picture and to attain the compression/extension of a gradation by finely taking the gradation in a density part having a frequency distribution higher than the density frequency distribution of the original picture and roughly taking the gradation in a density part having a lower frequency distribution. CONSTITUTION:The density histogram of original picture data is obtained. The gradation is more finely taken in the vicinity of density values (a), (b) relatively higher in the density frequency in the original picture data and the gradation is more roughly taken than the part higher in the density frequency in the vicinity of a density (c) relatively lower in the density frequency. Then the gradation is compressed and the loss in the quantity of the information relating to the gradation of the original picture data is reduced. In such a way, the gradation is varied according to a generation frequency, thereby, even if the density low in the frequency is digitized by roughly taking the gradation, it has little influence applied to a reproduced picture and the picture data is more compressed by the gradation taken roughly.
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