An image processing system includes a frequency decomposition unit adapted to decompose an image signal into a high frequency component and a low frequency component, a high frequency separation unit adapted to separate the high frequency component into an invalid component caused by noise and other valid component, a conversion characteristic calculation unit adapted to calculate a conversion characteristic on the basis of the low frequency component, a gradation processing unit adapted to perform a gradation processing on the low frequency component and the valid component on the basis of the calculated conversion characteristic, and a frequency synthesis unit adapted to generate an image signal on which a gradation conversion has been performed by synthesizing the low frequency component on which the gradation conversion has been performed, the valid component on which a gradation conversion has been performed and the invalid component.