An image data generating apparatus includes an extracting unit and a generating unit. The extracting unit extracts one or more pixels corresponding to a metallic-color region expressed by a metallic color, by using lightness and saturation of a read image and lightness and saturation of a captured image, the read image being obtained by reading a document having the metallic-color region, the captured image being obtained by capturing an image of the document. The generating unit generates image data in which the one or more pixels corresponding to the metallic-color region and extracted by the extracting unit are colored in the metallic color.