Joseph Allen , Jul 19, 2004; 12:08 a.m.
They scan the roll of developed film through the machine. It pops up the photos 6 at a time. The lab tech can then decide to lighten/darken each one (or leave it how the machine guessed was correct) and also adjust the color (cyan/red, magenta/green, yellow/blue). If the lab techs at the lab you described are paying attention and are reasonably good at your job, you shouldn't get dark portraits under the tree any more.