A web rendering engine, such as WebKit, takes a web page that is described structurally using HTML and a DOM and visually using CSS and transforms it into a series of painting commands and then passes these commands to the graphics stack.
A major responsibility of the graphics stack is rasterization: converting vector painting commands into color pixels on a screen. Rasterization also applies to text display. A single letter can consist of a chain of hundreds of curves. Rasterization produces a matrix of pixels of varying colors that gives users the impression of smoothly drawn text. The following picture shows the enlarged portion of a letter displayed on the screen: