Judging the quality of a depth map is hard when it is only colored by the depth because local details are lost. These details can become visible by computing normals and using them for lighting. An alternative to lighting is to simply display the normals by encoding them directly in rgb (as normals maps are typically done). Lighting is more flexible than coloring by normals because it also works together with other ways of coloring the depth data, eg by a colormap, solid color or an image from a color camera.