Edge enhancement methods based on derivative operations

TLDR: In this article, two methods for edge enhancement using optical derivative operations are described based on the polarization properties of the twisted-nematic liquid-crystal displays (LCDs).

Abstract: Two methods are described for edge enhancement using optical derivative operations. The proposed methods are based on the polarization properties of the twisted-nematic liquid-crystal displays (LCDs). LCDs traduce the image information in changes of the state of polarization of the light, which allows us to generate simultaneously a "positive" and a "negative" (i.e., a contrast-reversed) replica of the digital image displayed on the LCD. In both methods negative and positive replicas are at the same time imagined across a plane. In first case when the negative replica has a lateral differential displacement relative to the original one, an image with enhanced first derivatives along a specific direction is obtained. In the case when the negative replica is low-pass filtered, one obtains the Laplacian of the original image. Unlike the usual Fourier (coherent) image processing, the technique proposed here works with incoherent illumination. Validation experiments are presented.