The basic principle behind shape from texture is the distortion of the individual texels. Their variation across the image allows to estimate the shape of the observed surface. The shape reconstruction exploits perspective distortion, which makes objects far from the camera appear smaller, and foreshortening distortion, which makes objects not parallel to the image plane shorter. The amount of both distortions can be measured (shape distortion and distortion gradient) from an image.

To calculate the surface curvature at any point is far from trivial. Therefore, the surface shape is reconstructed by calculating the surface orientation (surface normal). A map of surface normals specifies the surface's orientation only at the points where the normals are computed. But, assuming that the normals are dense enough and the surface is smooth, the map can be used to reconstruct the surface shape.