Gouraud shading is a method used in computer graphics to simulate the differing effects of light and colour across the surface of an object. In practice, Gouraud shading is used to achieve smooth lighting on low-polygon surfaces without the heavy computational requirements of calculating lighting for each pixel. The technique was first presented by Henri Gouraud in 1971. These colour values are then interpolated along the edges of the polygons. To complete the shading, the image is filled by lines drawn across the image that interpolate between the previously calculated edge intensities.