An image processing method displays a simulation image of an image formed on a print medium under a first light-source color on a display under a second light-source color. The method includes an acquisition step of acquiring image data to be simulated in a format according to the second light-source color, a step of calculating a reflective color obtained when the acquired image data is processed to represent an image corresponding to the image data illuminated by an achromatic light-source color, a step of converting the first light-source color into the format according to the second light-source color, and calculating a glossy color of the image data based on the converted first light-source color, and a generation step of generating an image to be displayed by adding the reflective color calculated in the reflective color calculation step and the glossy color calculated in the glossy color calculation step.