An image output apparatus supplies output image data including color components of color materials to an image forming apparatus that prints an image represented by input image data using chromatic color material and/or achromatic color material. In a monochrome mode in which an amount of the chromatic color material is larger than an amount of the chromatic color material used in a neutral tone, the image output apparatus includes a gradation correction unit configured to correct gradation levels of the image data which includes the color components of the color materials and which has been converted using the color separation unit. The gradation correction unit processes the chromatic color material so that a value of the output image data corresponding to an intermediate value of intermediate image data obtained through the conversion using the color separation unit is equal to or smaller than a half of a maximum value of the output image data.