Abstract
In this paper, we examined a gradation that give a good impression based on impression assessments, and then we researched characteristics of the gradation focused on luminance-difference. Results showed that impression image improved with gradation increase. However, the tendencies are significant between 32 to 128 gradations, and then 128 gradations had luminance-difference of more than the JND. We found that a necessary gradation is 128 when a response curve of display device follows the JND. On the other hand, when that follows the gamma curve of 2.2, necessary gradation is 256.
