The normal map is sometimes called "Dot3 convex-concave texture map". Convex-concave and texture mapping are usually different from adding a disturbance to the normal of an existing model, and normal mapping should completely update the normal. Similar to bump mapping, it is also used to add details to shading effects without adding polygons. However, bump map is usually calculated according to a single gray image channel, while the data source image of normal map is usually a multi-channel image obtained from a more detailed version of the object, that is, the red, green and blue channels are regarded as a single color.

There are usually two variants of normal map, namely, object space normal map and tangent space normal map, and their difference lies in the coordinate system used for normal measurement and storage.

An interesting application of this technology is that the display effect of low polygon model is greatly improved by using the normal map table of high resolution model. Although Krishnamurthy and Levoy put forward the method of using the details of resolution model to create displacement maps instead of non-uniform rational B-splines in the article "Using smooth surfaces on dense polygonal meshes" in 1996, it was not until later that the more common triangular meshes were used. In 1998, two other papers put forward the transformation of polygon meshes with details from high resolution to low resolution as normal maps: Cohen et al.' s "keeping the appearance simple" in SIGGRAPH 1998 and Cignoni et al.' s "general method of restoring attribute values on simplified meshes" in IEEE Visualization' 98. In the first paper, a special constraint simplification algorithm is proposed, which tracks how to map the missing details to the simplified grid in the simplification process. In the second paper, a simple method of separating high-precision and low-precision polygonal meshes and a method of recovering lost details that is not affected by the low-precision model construction method are proposed. The latter method and its variants are still one of the methods used by most available tools at present.