Long-exposure video camera with digital memory

A digital field memory was used in a MOS video camera imager as an electronic variable shutter to obtain variable exposure time in the range from 1/5000 to 1/2 second. A 1.5 Mb field memory was used with a 280-kilopixel MOS imager. The memory was inserted between a gamma corrector and an encoder, so that quantizing noise was minimized. An inexpensive system was developed with 6-bit digitization for both luminance (Y) and colour-difference (C-Y) signals. The same digital circuit was used for a 370-kilopixel imager by adjusting the quality limit of a field picture. It is noted that imaging at the 1 lux level is possible in the 1/2-second long exposure mode because signal charges are accumulated in the imager for multiple fields to gain sensitivity. The signal readout from the imager is then sampled and held using the digital field memory