A device allows easy and unencumbered interaction between a person and a computer display system using the person's (or another object's) movement and position as input to the computer. In some configurations, the display can be projected around the user so that that the person's actions are displayed around them. The video camera and projector operate on different wavelengths so that they do not interfere with each other. Uses for such a device include, but are not limited to, interactive lighting effects for people at clubs or events, interactive advertising displays, etc. Computer-generated characters and virtual objects can be made to react to the movements of passers-by, generate interactive ambient lighting for social spaces such as restaurants, lobbies and parks, video game systems and create interactive information spaces and art installations. Patterned illumination and brightness and gradient processing can be used to improve the ability to detect an object against a background of video images.