A computer graphics effect that involves an image and a corresponding height map.

For each pixel in the image, a corresponding surface normal is calculated. Then, based on the location of the light source and angle of the surface normal, the pixel is shaded.

The result is a "three-dimensional" effect on the image, with shadows.

There are many ways to implement the algorithm; for example, for real time, quick shadings, the algorithm can be simplified (yes, this has been seen in many C64 demos =), with lookup tables, for example.

A GIMP plugin also exist for this effect; it is one of the Holy Plugins Everyone Must Master to make cool graphics.

One limitation of bump maps is apparent along silhouette edges of the bump mapped object. Since bump maps only change the surface normal of the object but not the actual shape, the silhouette will appear smooth, without bumps. A displacement map fixes this problem by providing an actual displacement along the surface -- the shape of the object is changed. However, displacement maps are much more computationally expensive than bump maps because the shape change complicates the determination of object visibility.

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