Gouraud

Gouraud shading is a method in computer graphics for rendering smooth shading on polygonal models. Named after Henri Gouraud, who introduced the technique in the early 1970s, it works by computing lighting at the vertices of each polygon and then linearly interpolating the resulting colors across the polygon’s surface. The process typically uses a local illumination model at each vertex, incorporating diffuse and specular components, and then blends those vertex colors as you move across the polygon using barycentric interpolation.

This approach is computationally efficient because it reduces shading calculations to the vertices rather than every pixel. It became a common technique in real-time rendering on early graphics hardware, where per-pixel lighting was too costly. Gouraud shading helps produce the appearance of curved surfaces on a mesh of flat polygons by creating gradual color transitions between vertices.

However, Gouraud shading can exhibit artifacts. Since lighting is only evaluated at vertices, highlights may not be accurately represented across the interior of large polygons, causing specular effects to appear to jump or shimmer as the viewpoint or lights move. The method is also sensitive to polygon density; finer meshes yield smoother results but require more geometry.

In comparison, Phong shading, which interpolates surface normals across a polygon and computes lighting per pixel, can produce more accurate and stable highlights but at greater computational cost. Gouraud shading remains a foundational concept in computer graphics, often taught to illustrate per-vertex illumination and piecewise-smooth shading.