An image processing apparatus that generates image data for generating an image by overlaying a second image upon a first image, the image processing apparatus comprising: a color information obtaining unit configured to obtain color information including a diffuse reflection color and a specular reflection color that differs from the diffuse reflection color; a lower-layer-image data generating unit configured to generate first image data indicating a first image where a plurality of macro regions, each comprising a diffuse reflection region in which a white color amount is to be laid out and a specular reflection region in which a silver color amount is to be laid out are laid out at a resolution such that each macro region is perceived as being a single region; and an upper-layer-image data generating unit configured to generate second image data for generating the second image, where the diffuse reflection color is laid out in the diffuse reflection region and the specular reflection color is laid out in the specular reflection region, based on the color information and the first image data, wherein the lower-layer-image data generating unit obtains the first image data, in which a specular reflection proportion is different to a diffuse reflection proportion; wherein the specular reflection proportion is a proportion of the reflection intensities of incident light at the diffuse reflection region and the specular reflection region in a specular reflection direction out of reflection directions of the incident light, wherein the diffuse reflection proportion is a proportion of the reflection intensities of incident light at the diffuse reflection region and the specular reflection region in a non-specular reflection direction that is different from the specular reflection direction, and wherein the lower-layer-image data generating unit decides an area proportion between the diffuse reflection region and the specular reflection in the first image by comparing the color information with a gamut of a diffuse reflection color and a specular reflection color in accordance with the area proportion, based on the diffuse reflection color and the specular reflection color, and generates the first image data based on the area proportion. a color information obtaining unit configured to obtain color information including a diffuse reflection color and a specular reflection color that differs from the diffuse reflection color; a lower-layer-image data generating unit configured to generate first image data indicating a first image where a plurality of macro regions, each comprising a diffuse reflection region in which a white color amount is to be laid out and a specular reflection region in which a silver color amount is to be laid out are laid out at a resolution such that each macro region is perceived as being a single region; and an upper-layer-image data generating unit configured to generate second image data for generating the second image, where the diffuse reflection color is laid out in the diffuse reflection region and the specular reflection color is laid out in the specular reflection region, based on the color information and the first image data, wherein the lower-layer-image data generating unit obtains the first image data, in which a specular reflection proportion is different to a diffuse reflection proportion; wherein the specular reflection proportion is a proportion of the reflection intensities of incident light at the diffuse reflection region and the specular reflection region in a specular reflection direction out of reflection directions of the incident light, wherein the diffuse reflection proportion is a proportion of the reflection intensities of incident light at the diffuse reflection region and the specular reflection region in a non-specular reflection direction that is different from the specular reflection direction, and wherein the lower-layer-image data generating unit decides an area proportion between the diffuse reflection region and the specular reflection in the first image by comparing the color information with a gamut of a diffuse reflection color and a specular reflection color in accordance with the area proportion, based on the diffuse reflection color and the specular reflection color, and generates the first image data based on the area proportion.