An image processing apparatus processes input image data and generates output image data. The image processing apparatus includes a feature-value calculating unit, an output-gradation-number setting unit, and an image processor. The feature-value calculating unit calculates a feature value from the input image data. The output-gradation-number setting unit sets, as the number of output gradations, any one gradation number of candidates for the number of output gradations based on the feature value calculated by the feature-value calculating unit. The image processor processes the input image data and generates the output image data having the number of output gradations which is set by the output-gradation-number setting unit.