In order to scan a relatively small window (F) in the image zone (ZI) of a charge transfer device, a series of prior transfers (B.sub.1, B.sub.2, B.sub.3) are performed moving from the image zone to the memory zone (ZM) to move the leading edge of the window until it is adjacent to the output shift register (RD). The lines of the window may then be read conventionally (B.sub.4) omitting any reading of the lines that come before or after. This considerably reduces the delay (between steps B.sub.1 and B.sub.4) between image acquisition and signal processing, without altering the frame frequency which remains fixed at 50 Hz, for example.