[old_tv_nut]

As Ed in Tx says, these machines were self-contained. They had a photocell to scan the original, and analog circuits to compute the correct amount of cyan, magenta, yellow, and black. This controlled four beams of light to expose four black and white transparencies for the four printing plates. They were tedious to adjust to match the properties of the inks and printing press, so they were used to standardize the process for a printing plant that did lots of work on the same materials. Hence, they were first developed in conjunction with the very largest printing plants that did national magazines like LIFE and Time. They cost something like $200,000 each.

Due to the slow process of adjusting and the cost, they could not be used by an individual photographer on an image-by-image basis. Any artistic modifications to a photograph had to be done the old fashioned way first, and then this machine would be used to get the most consistent printed reproductions.

The famous photographer Ansel Adams lived long enough to see these machines, and speculated that the technology might some day allow manipulation of color photographs equivalent to what he did with black and white; but he never had personal access to a scanner, computer, spectrophotometer, and printer, all of which you can have at home today.

Today we have all the devices and software that allow much quicker adjustment of the process when different paper, inks, or printing machines are used. Still, it's something of a difficult and not entirely perfect process, but much quicker and easier to measure and correct for errors.

Drum scanners are still considered to be the highest quality devices for scanning transparencies today, but since most photography is digital, there is much less volume of work for them.