Abstract: Television apparatus for producing signals for displaying simultaneously a succession of separated images of an object moving over a selectable time period in an otherwise substantially static scene so that the trajectory of the object can be viewed. The effect is achieved by storing, at the start of the selectable time period, a television frame in a suitable storage device and periodically comparing the stored frame with television frames arriving subsequently during the selectable time period, and upon detection of differences between corresponding picture elements of the stored and subsequently arriving frames, substituting the picture elements that caused the detected difference in the stored frame. The system identifies such substituted picture elements and ensures that the same picture elements are not again substituted during the selectable time period.