Methods for edge enhancement in color images based on derivative operations

Abstract

We present optical methods for edge enhancement in color images using optical derivative operations (first order derivative and Laplacian operator). The proposed methods is based on the polarization properties of liquid-crystal displays (LCD) and on the capacity of digital micro mirror devices to generate a (positive) copy of the digital image used as input, and simultaneously a complementary color replica of it. In the proposed optical setup the negative and positive replicas are at the same time imagined across a plane. First we analyzed the 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 Fourier, our proposal works with incoherent illumination and does not require precise alignment, and thus, it could be a useful tool for edge extraction/enhancement in large images in real-time applications. Validation experiments are presented.