Creating 3D effects with maps in GIMP
GIMP adds texture and other three-dimensional effects to images through the use of secondary maps that affect the original image on a per-pixel basis.
Many images lack depth, making them seem flat, and thus lifeless or "false." For realistic 3D effects, GIMP provides a set of filters that use the pixel brightness values contained in secondary maps to modify the original image. These methods are applicable both on a small scale, in image details, and to the entire image.
The Bump Map filter offers a way to create very attractive three-dimensional effects. To do so, brightness and position data are processed with brightness data from another layer (the bump map), usually causing shifting and additional changes in brightness.
The Bump Map filter  (Filters | Map | Bump Map) is relatively simple, as Figure 1 shows. The filter always acts on the current image when it is called and uses a "virtual" light source that modulates a three-dimensional effect using light and shadow.
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