1. An image processing device, comprising: a correction-reference-amount determining device to detect a degree of a level change in original image data and to generate correction-reference-amount data indicating an reference amount for correction by sharpness processing in accordance with the degree of the detected level change; a correction-amount calculating device to calculate a correction amount in accordance with a pre-determined correction-amount determining pattern, based on the correction-reference-amount data; and a sharpness processing device to perform sharpness processing on the original image data in accordance with the correction amount to generate correction image data, the correction-amount determining pattern having a characteristic that the correction amount varies in accordance with the magnitude of the correction reference amount.