1. An illumination estimation device, comprising: a memory storing instructions; and at least one processor configured to process the instructions to: extract an object area from a multispectral image, the object area being an area, including specular reflection, of an object; estimate information representing a subspace that approximates a distribution of observation values in a spectral space, as distribution characteristics, the distribution characteristics being characteristics of a spreading manner of the observation values in the object area within the spectral space; select a distribution characteristic to be used from among the estimated distribution characteristics depending on the number of dimensions to be reduced, the number of dimensions to be reduced being determined in advance by a light environment; and estimate spectral characteristics of illumination based on the subspace information to be represented by the selected distribution characteristic.