Optical wavelet processor for producing spatially localized ring-wedge-type information

Mark O. Freeman; Adam S. Fedor; Brett D. Bock; Kenneth A. Duell

doi:10.1117/12.140913

12 January 1993 Optical wavelet processor for producing spatially localized ring-wedge-type information

Mark O. Freeman, Adam S. Fedor, Brett D. Bock, Kenneth A. Duell

Proceedings Volume 1772, Optical Information Processing Systems and Architectures IV; (1993) https://doi.org/10.1117/12.140913
Event: San Diego '92, 1992, San Diego, CA, United States

Abstract

Ring-wedge detectors are known to produce a useful feature set for certain types of pattern recognition. Their major shortcoming is that they measure global features. We present an optical processor, based upon the computation of a two-dimensional wavelet transform, which overcomes this limitation. By using wavelet functions that are essentially compact in the space domain we generate an output that consists of a mosaic of spatially localized bandpass components. Consistent with the nature of wavelets, the radial (ring) frequency components, are organized into constant-Q (f₀/(Delta) f) bands. The angular (wedge) frequency content is divided into a number of equal-width bands which cover the full 0 - 180 degree(s) range. The radial information is obtained by using a feedback iteration loop which scales the input image by a fixed factor for each time around the loop. By introducing a tilt in the Fourier plane of the feedback loop, we arrange for the space-domain representations of each scaled input to be spatially separated without altering the position of their Fourier transforms. In this way, all of the radial frequency bands can be extracted with a single wavelet filter. A diffraction grating is introduced into the optical path after the scaling loop to replicate the Fourier information M times. The angular information is extracted using M filters in parallel-- one for each wedge component. The filter outputs are minified consistent with Nyquist theory for their reduced bandwidths to produce an output whose space-bandwidth product is roughly the same as that of the input image. We present the design of the optical system along with some initial experimental results.

Citation Download Citation

Mark O. Freeman, Adam S. Fedor, Brett D. Bock, and Kenneth A. Duell "Optical wavelet processor for producing spatially localized ring-wedge-type information", Proc. SPIE 1772, Optical Information Processing Systems and Architectures IV, (12 January 1993); https://doi.org/10.1117/12.140913

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