This thesis is concerned with the design of a computer graphics system for in particular artists, and in general surface designers (where surface design refers to the design of 2Dimensional surfaces, e.g. wallpaper, carpets and fabrics). It is argued that the artist tends to be tentative both in terms of plans of action and also the meaning of the image. This is reflected in changes of mind that have consequences on the artists plans and on the structure of the perceived image (i.e. an image perceived in one way may be seen differently later on). On both counts, it is argued, conventional vector based computer graphics does not possess the desired flexibility. Raster graphics employing a 'bitmap' to represent the picture for display offers new potential and greater flexibility. In particular it permits a view of interactive graphics, described as "communicating interpretations" in which the user is seen as being involved in communicating features in a visual scene shared by the man and the machine to the machine. In so doing the user is able to operate on objects in the picture as and when they are perceived. A language (GLIMPS) is described which not only permits the user to generate pictures but also includes facilities for extracting and operating on perceptual features of a picture. GLIMPS makes it possible for both "physical" (region) and "non-physical" (figure on ground) properties of the 'bitmap' to be handled. In conclusion it is argued that the "communicating interpretations" view is more generally applicable in interactive computer graphics.

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