[OPTICAL REVIEW Vol. 4, No. 5 (1997) 539-542]

Optimal Incoherent Filtering for Distortion-Invariant Image Recognition*

Jianping DING,1 Masahide ITOH2 and Toyohiko YATAGAI2

1Physics Department, Nanjing University, Nanjing 210008, China, 2Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, 305 Japan

(Received May 9, 1996; Accepted June 11, 1997)

An optimal incoherent filter is proposed for distortion-invariant correlation. The optical transfer function (OTF) of the correlator is specified as a realizable phase-only term which is optimized by the simulated annealing algorithm. The phase-only OTF is used in image recognition to produce a sharp peak response and can be generated by dual-filter synthesis. Image recognition is achieved by subtracting two spatially incoherent correlation outputs produced from a positive and negative filters with an input image. Computer simulations show that the proposed correlator can yield a sharp correlation peak with excellent distortion tolerance.

Key words : image recognition, optical transfer function, incoherent optical correlator, distortion-invariant correlation

*Presented at 1996 International Topical Meeting on Optical Computing (OC '96), April 21-25, Sendai, Japan.