The Ray Tracer Challenge

Anti-aliasing

Because pixels are not infinitely small, diagonal lines will tend to be rendered as stairsteps, or jaggies. The following illustration shows a zoomed-in view:

This phenomenon is called aliasing, and a lot of effort goes into working around it in production-quality imagery. One such anti-aliasing technique renders the image at much higher resolution (double, triple, or more), and then requires a separate image editor to resample the picture to a smaller resolution. This essentially averages the values of adjacent pixels, and helps smooth those jagged stairsteps.

You can anti-alias in a single step, though, using a technique called ...