Raster tab controls raster layer display properties.
Use grayscale – redraws layer in 256 shades of grey.
...
Select Raster Data Type – opens a new window that lets you utilize additional information contained in your raster image.
There are 3 predefined types of raster images (Height, Aspect and Slope). In addition you can configure aspect vectors styling as well as their size and spacing.
Gradient – specific raster layers that have values stored in pixels (like height layers or density maps) have to be styled using gradients. Click Edit.. to open Gradient Editor.