Directional filtering as a multi-purpose tool in image processing

Directional filtering is commonly known as a technique for selective linear enhancement. In addition to this traditional utility, we present in this paper some examples demonstrating that it can be used as a multi-purpose tool in image processing, by adjusting its parameters. These examples show that: (1) applying directional filtering in conjugate directions simultaneously can lead to the enhancement of specific conjugate linear features on an image, which is useful in interpretation of geophysical and Landsat images, satellite and aerial photographs that contain many conjugate linear features; (2) directional filtering can be used as illuminating sources to produce shaded relief images that show 3D effect; by combining the directional filtered result with its original image, this 3D effect becomes much more profound; (3) the directional filtered result can be weighted by different factors, which allows some subtle features on an image to be identified