Abstract: Improvements and modifications are described to an image analyzing system in which an image of a field under analysis is displayed on a television monitor screen and features can be edited by adding or subtracting feature content to or from the display (and corresponding signal content to or from the signal which is to be processed for analysis) using a light pen.One improvement provides for straight line interpolation between points in the display selected by the light pen during successive frame scans, so that a continuous trace and therefore corresponding signal is produced in the display corresponding to the path traced out by the light pen.Another provides for an alarm signal to be generated if the storage facility used for storing the locus of the trace to allow its reconstruction during successive frame scans, becomes more than a given percentage occupied.