1. An image processing device comprising: a converting section for converting image data; a designating section for designating a conversion characteristic of gradation conversion of the image data; and a control section for controlling a conversion characteristic of the converting section such that a gradation of the image data is converted in accordance with a conversion characteristic which is designated via the designating section, and for one of reconverting image data which is converted by the converting section and controlling the conversion characteristic of the converting section, such that changes in a ratio of a difference, of each of color components, with respect to gray of each pixel of the image data, which changes accompany conversion of the gradation of the image data in accordance with the designated conversion characteristic, are corrected.