1. Apparatus for generating a processed video signal representative of an image of a body, comprising: a source of radiation directable at the body; means for detecting radiation received from the body; means for converting the detected radiation into an electronic video signal; means for storing a series of frames of said video signal as pixel values at respective pixel positions; means for determining, for each frame, i, of the series, an average pixel value, S.sub.i, for the frame; means for determining, for each frame, of the series, an enhancement value, k.sub.i, as a function of the average pixel value, S.sub.i, for the frame; means for combining the pixel values of the pixels of each of the stored frames, i, with the enhancement value k.sub.i for the frame to obtain enhanced pixel values; and means for combining the enhanced pixel values of corresponding pixels of the frames of the sequence to obtain a processed pixel value at each pixel position.