1. An image processing apparatus, comprising: a feature vector extraction unit configured to extract feature vectors from a learning image; a first feature vector classification unit configured to classify the feature vectors extracted by said feature vector extraction unit into a first cluster based on a first classification method; a representative vector generation unit configured to generate representative vectors of the feature vectors included in the first cluster classified by said first feature vector classification unit; a representative vector classification unit configured to classify the representative vectors generated by said representative vector generation unit into a second cluster which is different from the first cluster based on a second classification method which is different from the first classification method; an association unit configured to associate the representative vectors with the second cluster; and a storing unit configured to store a result associated by said association unit as a lookup table.