This image compares a G1 surface scheme to the cubic interpolant. The data was a sampling of the torus (50 samples, 100 triangles). The left column shows a G1 surface fit to this data; the right column shows the cubic interpolant fit to this data.
The top row shows shaded images of both surfaces. Despite being only approximately G1, the cubic interpolant surface appears smoother than the corresponding G1 surface.
The bottom row shows curvature plots of the surfaces. Both images are shaded with the Gaussian curvature of the surface. The Gaussian curvature of a torus would be blue on the inside, yellow on the outside, and green on the top and bottom.