| 摘要 |
PROBLEM TO BE SOLVED: To perform a gradation reduction excellent visually and in terms of signal processing, and optimized according to each image.SOLUTION: A gradation reduction device 1 comprises: a frequency resolution part 10 which generates a plurality of frequency band components from an original image; a noise threshold determination part 20 which determines a plurality of noise thresholds on the basis of a power ratio of the space highest frequency band component against a whole band component; a noise removal image generation part 30 which generates a noise removal image from the frequency band components and the noise threshold; a gradation reduction initial information generation part 40 which generates a histogram of the noise removal image and a gradation conversion table; a gradation reduction part 50 which generates a gradation reduction image by the Lloyd-Max method and a plurality of inverse quantization tables; a gradation restoration image generation part 60 which generates a gradation restoration image by applying the inverse quantization tables to the gradation reduction image; and a gradation reduction image determination part 70 which outputs a noise threshold used for generating a gradation restoration image having the minimum difference with the original image and a gradation reduction image corresponding to the gradation restoration image having the minimum difference with the original image. |
