Tan quotes evidence from cortical channel studies that  Gabor  functions can be used as features for texture recognition. The Gabor filters are not rotation-invariant, while most textures are. The author has developed rotation-invariant filters based on the Gabor filters. Initially the filters are integrated over the rectilinear coordinates to obtain functions dependent only on the frequency and the inclination. These clearly yield periodic functions over the inclinations. The Fourier transforms of these periodic functions have coordinates independent of the inclination and hence serve as rotation-independent features for texture.

These filters have been used to distinguish texts written in various alphabets, so that different features of the texts can be extracted depending on the recognized script. The author discusses the success of the recognized features in distinguishing Chinese, English, Greek, Russian, Persian, and Malaysian scripts as well as in distinguishing various Chinese and English fonts.