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I see photoshops offering drum scanning to 1 Giga Pixels and even more. How is a machine from the past able to extract so much information? In addition to how the scanning process functions, does anyone know how lab techs in the 80s 90s handled extremely large amount of data (several GBs) generated by the scanner?

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    In the 80s & 90s many drum scans were still transmitted as analog data over phone lines. There was a machine at the other end that exposed (using light that was flickering with the intensity of the analog signal) photo sensitive paper as the analog signal was received. The exposed photopaper was then developed in the darkroom just as a print from an enlarger would have been developed.
    – Michael C
    Mar 13, 2021 at 6:22
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    This promotional film from 1937 shows how it all started.
    – Michael C
    Mar 13, 2021 at 6:35
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    This video shows where it wound up.
    – Michael C
    Mar 13, 2021 at 6:54

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The drum scanner operated by affixing a film or print image to the outside of a cylinder of clear glass. The drum was powered up causing it to spin at high speed. A light source located inside the cylinder outputs a focused spot of light that passes through the glass cylinder and traverses the film.

The color and intensity of this beam of light is thus modified by film. This emerging light then plays on a photo multiplier tube. A photo multiplier tube is old-school, a cousin of the old-fashion radio / TV glass enclosed tubes. Light hitting this tube converted light energy into an electric charge. The photo multiplier was outstanding due to its ability to react to minuscule changes in light intensity by outputting an amplified antilog signal.

The location of the spot of light playing on the film is mechanically moved. The photomultiplier is also moved in step with the focused light source. These movements and the spin of drum generate an analog representation of the film’s image. To record a color image, three scans are made by passing the light through red, green and blue separation filter. If the image is a print on paper, the light reflects back into the cylinder after traversing the print emulsion. It is then directed to a photomultiplier inside the cylinder.

The analog signal could be used by devices that exposed photo film or photo paper. Some accepted the analog signal, otherwise the signal was converted to a digital signal. These exposing devices were constructed using red, green, and blue laser light sources that were caused to trace a path across film or paper. Various analog and digital storage methods were used. These included giant 10 inch floppy disks and various hard disks not far removed from the ones used today.

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  • Thanks for the answer, is there a name for the "exposing devices" that print on photo paper/film for later development. Is there any use cases for them today?
    – zjwang
    Mar 13, 2021 at 19:06
  • The Durst Lambda is a continuous roll-to-roll single beam, three-laser (RGB) exposure system exposing color photo paper of large size making a print with superior quality.
    – Alan Marcus
    Mar 13, 2021 at 19:40
  • @zjwang Pretty much every photo finisher that prints digital files onto photosensitive paper these days uses colored lasers to expose the photopaper. The prints I get from M-Pix Pro (a/k/a Miller's and M-Pix) are made this way. I don't know whose machines they use, but they're all laser based these days.
    – Michael C
    Mar 13, 2021 at 19:47
  • Cymbolic Sciences LightJet printers set the standard for true photographic quality expose conventional images making 0x50"/102x127cm prints (now under the Canon name).
    – Alan Marcus
    Mar 13, 2021 at 20:23
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I'm going to address one aspect of your question, since most of the rest has already been answered.

I see photoshops offering drum scanning to 1 Giga Pixels and even more. How does it a machine from the past able to extract so much information?

The one gigapixel scans are usually of large format negatives. There's a LOT more information that can be contained in a high quality piece of film that is 8 x 10 inches (20 x 25 cm or 200 x 250 mm) than in a 36 x 24 mm frame of the exact same film in 135 format ("35mm").

The surface area of an 8x10 negative is roughly 50,000 mm².
The surface area of a 135 negative is 864 mm².

One 8x10 negative can contain the same amount of information as 58 frames of 35mm film!

A one gigapixel scan of an 8X10 format image translates into about 17MP per any 36x24 mm area within it. Two gigapixels for an 8x10 format would be about 35MP for 135 format, and so on.

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A partial answer:

Those scanners (in begin of 90s) are managed by minicomputer (power of PGP-11) and store digitised images on magnetic tape. For example such scanner produce for 10" photos image with average size 1GB and store the information on magnetic tape like this. The read/write unit is something like this.

About the position of the lamp - it can be also inside when you scan film or plate.

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