Application of Walsh filters and subsequent angular-stitching for edge enhancement

Abstract

In common edge-enhancement techniques, mostly employed in digital image processing, all the edges of an object are enhanced simultaneously. Selective edge enhancement, a well-known technique in optics, on the other hand, is useful for controlled image representation and structural analysis of the images with applications in biology and chemistry. A simple yet versatile method for selective edge enhancement using a spatial bunch of filters, known as Walsh filters, applied in the Fourier domain has been presented in this paper. The method has been tested on different types of images such as camera images, and scanning electron microscope images. Experimental results with a half-circular object have been presented using reflective spatial light modulators (SLMs). After obtaining selective edges, Walsh filters have been rotated for ‘angular stitching’ to enhance edges in all possible radial directions. This makes this method superior to all previous selective edge enhancement methods using SLMs since it can be tuned to provide both selective or overall edge enhancements depending upon the situation.