When a program renders a picture on a display device, it must compute a color for each pixel on the display. Computing the color for a pixel involves taking samples from the model or scene being drawn. A display screen has a finite number of regularly-spaced pixels, which means that a rendering program will take a finite number of samples from the model. Aliasing occurs when the finite number of samples do not contain enough information to draw an accurate picture of the model.

The next three slides demonstrate sampling.