Smear can be minimized by careful design and the use of overflow drains. There can be a considerable difference in smear resistance among different CCDs, even of the same type. Pixel pushing Once the charge is accumulated, it needs to be serialized as a video signal. CCDs act as bucket brigade shift registers-each CCD element can store a charge and pass it along to its neighbor. All CCD chips share a common operational pattern.
Charges accumulate on pixels during the field time.
At the end of the field, the charges are rapidly moved from the active pixels into some type of storage. During the following field, the stored charges are marched out, one after the other, to form the field's video signal. During blanking, the picture shifts down directly through the active pixels into the field store, where it is serialized at leisure. Because active pixels are also shift registers, FT cameras use a rotating shutter to block light during the transfer. With these shutters, FT chips show no smear-but if the shutter fails in the open position, smear is apparent.