Years ago before digital photography and even today, photographer and design house that does ads and photos were shot on slides in 35mm or larger format, we all would rely on drum scanners to scan our images into digital format to use in Photoshop or what ever DTp program to do our layout and post production.
These drum scanners are the defacto standard for years but of course in the last 10 yrs or so, there are those flat bed type too and I am not talking those you buy in Sim Lim Sq. I am talking about those high end types that cost about $50,000. Like the drum scanner , these flat bed ones all scan at super high resolution of 12,000 dpi !!! They can be exported to CMYK or RGB colour format. They cost more to scan but they gives me the best resolution to work with. All those desktop ones you can buy from the lousy entry level flat bed scanner you buy at SLS for about $100 tat claim they can give you slide scanner feature to those Nikon Cool Scan. The Drum scanner and high end flat bed models kicks ass. no contest! heh
Oh by the way, how does a drum scanner work? One model I have seen often has a transparent glass cylindrical barrel. You will first clean the slide or negative in some cleaning solution to clean it of any dust..etc. Then it is carefull place on this cylindrical barrel and then then a larger glass cylindrical wraps around the first cylindrical barrel and sandwich the film in place. And then it spins at a high rotation speed while a special lens reads and a light source illuminate the slide as the cylindrical barrels spins.