Abstract: An interactive data retrieval system based on a personal computer is provided which comprises a database and a CD-ROM which is arranged to select and display visual images of product literature of interest to a user such as an architect for example. The database contains details of the illustrated products and the manufacturers of the products. A modem is provided to enable the user to communicate with the manufacturers of the displayed products and to receive updating information which is stored in the database. The display of a selected image may be aborted at any time by the user, and in order to facilitate comprehension of the image as quickly as possible whilst maximising the ultimate resolution of the image, the resolution of each displayed image is gradually increased during the display process. This is achieved by initially displaying the image in the form of blocks of identical pixels.