The contrast between previous scanners and the new gray-scale machines is as clear as black and white. TIFF & EPSF and halftones (shooting thru special screens).
Halftones are created thru processes such as PMT photo-
mechanical - one method uses a pastboard metaphor, which produces resolutions of up to 100lpi or a process which goes directly onto a negative, producing image up to 150lpi quality.Dithering & dithering matrix, bi-level scanning.
Gray-scale scanners are device independent-excellent graphic of bit-maps in depth.
Scanner buying guide (Pg 114). Good graphic of the inside of the scanner (Pg 118).