The activity of a television image can be used to control the rate at which television frames are transmitted resulting in improved usage of a television channel. The frames are transmitted at a reduced rate but are presented at the viewing end at the normal rate of thirty frames per second. The improved channel utilization comes about by combining several reduced rate television signals and transmitting them over a single television channel. This report investigates possible measures of activity and the use of the measure to control the frame renewal rate and examines the success of a simulation of a communication system in which the frame renewal rate is controlled by image activity. It is demonstrated that image activity can be successfully used to control a communication system which transmits still or slowly varying, i.e. low activity, pictures.