1. A method of image retrieval, the method comprising: dynamically selecting one of two types of matrixes to be used to weight, based on relevance feedback, a plurality of feature elements for image retrieval, the selecting being based on both a number of previously retrieved relevant images and a length of a feature vector including the plurality of feature elements; and transforming the feature elements to a higher level feature space if the selected one of the two types of matrixes has sufficient information for transformation, but leaving the feature elements untransformed if the selected one of the two types of matrixes has insufficient information for transformation, wherein the selected one of the two types of matrixes having sufficient information for transformation is decomposed as W=P T ΛP, where P is transforming matrix, and Λ is weighting matrix; whereas the selected one of the two types of matrixes having insufficient information for transformation is simply the weighting matrix Λ.