1. A pose estimation method comprising the steps of: a) measuring reflectivity or color at every point of a reference object under varying illuminations to produce a plurality of illumination variation textures, each representing a brightness value of said every point of the reference object, and calculating basis textures approximating said illumination variation textures; b) extracting feature points from said reference object and extracting feature points from an input image of a target object corresponding to the feature points of the reference object; c) creating a plurality of pose candidates from the extracted feature points of said reference object and the extracted feature points of said input image; d) creating, for each of said pose candidates, an image space of basis images representing brightness values of a plurality of two-dimensional images of said target object which would be obtained if said target object were placed in the same position and orientation as said each pose candidate and illuminated under varying lighting conditions by projecting said basis textures onto said image space of said target object; e) detecting, for each of said pose candidates, an image candidate within said image space of basis images by using said basis textures and determining a distance from the image candidate to said input image of said target object; and f) selecting one of the pose candidates corresponding to the image candidate whose distance to said input image is smallest.