Waterhouse Stops / Debrie
Numerous entirely automatic systems have been devised by printing machine manufacturers. Some printers have a separate 35mm band of card with holes of different sizes punched in it to let different amounts of light through. These are sometimes called Waterhouse stops (see Figure).
The cueing system causes the band to move at each light change varying the light as required. This was the first system to be used for colour grading as colour filters can be stuck over the holes as well.
Although this system was used from about 1915 it is still in use today on some slow optical printers. Another system uses differing resistances in series with the lamp to vary the brightness of the lamp at each light change.
The cueing system changes the resistance with switches. Some system is necessary
to record the sequence of
resistances needed.