Gouraud shading

If a mesh covers more pixels in screen space than it has vertices, interpolating colour values from samples of expensive lighting calculations at vertices is less processor intensive than performing the lighting calculation for each pixel as in Phong shading.

The problem is easily spotted in a rendering which ought to have a specular highlight moving smoothly across the surface of a model as it rotates.

While this problem can be fixed by increasing the density of vertices in the object, at some point the diminishing returns of this approach will favour switching to a more detailed shading model.

Both the linear and hyperbolic variants of interpolation of colors from vertices to pixels are commonly called "Gouraud shading".

Any linear interpolation of intensity causes derivative discontinuities which triggers Mach bands, a common visual artifact of Gouraud shading.