Liquid crystal polarization-converting devices for edge and corner extractions of images using optical wavelet transforms

Optical properties of radially polarized light generated by liquid crystal (LC) polarization-converting devices with two LC molecular orientations ((plus-minus)180° and (plus-minus)90° twist modes) are measured and the applicability to optical wavelet transforms (WTs) are discussed. It is found that the radially polarized lights in both the (plus-minus)180° and (plus-minus)90° twist modes can be regarded as wavelets. Based on the principle of WT, feature extractions of a simple binary image are carried out by applying the LC polarization-converting device to a shadow-casting system. Unique feature extraction properties of the shadow-casting system using the LC polarization-converting device and a LC microlens array are discussed. It is experimentally confirmed that edge and corner features are successfully extracted using the LC polarization-converting device with (plus-minus)180° and (plus-minus)90° twist modes, respectively.