CGI or Computer-Generated Imagery is the field of modern animation in which pictures are developed by programs in powerful computers, animated and then transferred to visual media for viewing. The earliest example of a fully rendered computer generated sequence in Doctor Who occurs during the opening pre-title sequence of 1987's Doctor Who television story Time and the Rani. This sequence and the title sequence that followed it were created by CAL Video at a cost of £20,000. This sequence included a computer-generated model of the TARDIS, the first time a three-dimensional CGI model of the police box had been created. Previous stories had featured a 2D computer drawn model, as in Logopolis. In 1996 for the US/UK co-production of the Doctor Who television movie, another CGI based title sequence was created. Again a TARDIS/police box model was created for this sequence and a modified logo, based on the Season 7 - Season 10 logo.
In the years since, advances in computer power and programming have reduced the costs of CGI to the point where it is less expensive than traditional model making and other animated techniques.[source needed]