The cartographer has to selectively adjust light direction and brightness of important landforms when producing shaded relief. For shading derived from a DEM, necessary local adjustments are achievable by two different methods:
Photoshop allows for the selective correction of gray values or to combine multiple shaded relief images created with differing illumination direction. This is a rather tedious, but currently the only viable method.
An alternative is the use of software specificially developed for cartographic relief shading.
A Concept for Local Adjustments
At the Institute of Cartography (ETH Zurich), development of an interactive relief shading application is underway. Still at the prototype stage of development, it allows the cartographer to locally adjust several shading parameters, including light direction.
For applying local adaptations to shaded relief, the software uses the concept of fences, an interface metaphor borrowed from CAD applications. To use fences, the user draws a bounding enclosure to isolate a portion of a DEM. Within the fenced area parameters are adjustable to locally alter the appearance of the shaded relief.