  This paper presents a novel descriptor named Region based Extensive Response
Index Pattern (RETRaIN) for facial expression recognition. The RETRaIN encodes
the relation among the reference and neighboring pixels of facial active
regions. These relations are computed by using directional compass mask on an
input image and extract the high edge responses in foremost directions. Further
extreme edge index positions are selected and encoded into six-bit compact code
to reduce feature dimensionality and distinguish between the uniform and
non-uniform patterns in the facial features. The performance of the proposed
descriptor is tested and evaluated on three benchmark datasets Extended Cohn
Kanade, JAFFE, and MUG. The RETRaIN achieves superior recognition accuracy in
comparison to state-of-the-art techniques.
