So yesterday you subcloned 1 kb fragments sheared from 20 40-kb cosmid inserts into an M13 vector. Over the next few days you get to pick 1,000 plaques from each library. Lots of coffee and some great tunes on the boom box may help this process, assuming your eyes don't cross too much. The plate-handling system can accommodate 72 rectangular petri dishes at once. For bacterial colonies, the plate is illuminated from above.
Colonies show up as bright points against a dim background.
A red filter further discriminates blue and white colonies. A graphical interface allows background subtraction control and selection of features based on brightness, roundness, and separation from other features. If the average number of positive clones per plate is low, plate-handling and imaging time is increased. Less than 3 percent of the output cultures will be mixed or failed inoculations. Colonies or plaques are picked from the imaged plate by tungsten needles.