[OPTICAL REVIEW Vol. 4, No. 5 (1997) 561-566]

A New Method for Rotation and Brightness Invariant Pattern Recognition Based on Modified Multiple Circular Harmonic Expansions

Wanji YU,1 Takumi MINEMOTO1 and Takao IKUNO2

1Graduate School of Science and Technology, Kobe University, Rokko-dai, Nada-ku, Kobe, 657 Japan, 2The Faculty of Engineering, Kobe University, Rokko-dai, Nada-ku, Kobe, 657 Japan

(Received May 9, 1997; Accepted June 30, 1997)

A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals.

Key words : pattern recognition, circular harmonic expansion, matched filter correlator, joint transform correlator