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I've come across references to digital minilabs, which project digital photographs onto standard photographic paper and then develop them using the same chemical processes as traditional film development. (See, for example, http://en.wikipedia.org/wiki/Minilab#Digital_minilab and http://en.wikipedia.org/wiki/LightJet.)

How does this projection actually work? Typical digital projectors almost certainly lack the resolution and color range to faithfully reproduce digital images on photo paper. The LightJet article loosely describes a process involving lasers.

Does anyone know of a detailed technical explanation (outside of the ones in the linked Wikipedia articles)?

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I suspect most minilab makers are going to consider that proprietary information so you're not going to learn much about it. –  cabbey Jun 29 '11 at 4:34
@cabbey: I bet they have patents. –  mattdm Jun 29 '11 at 12:24

2 Answers 2

A typical digital projector has to project the whole image at once. My guess is the minilab digital printers work by sweeping a laser beam across the image one line at a time, in a simmilar fashion to how old cathode ray tube TVs and monitors work. That way they can get a much higher resolution image than a typical digital projector, which shines a bright (non-laser) light through an LCD grid of pixels.

A line-sweep digital projector has no "pixels" and the resolution of the projected image is only limited by the diameter of the laser beam and how precisely it can be aimed.

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Having seen lots of the prints that result when they have issues, I can say that your guess is correct, especially for the high speed continuous roll printers. ;) –  cabbey Jun 29 '11 at 17:44

Minilabs aren't cheap, and wouldn't use a typical digital projector.

The specifications sheet for the Fuji Frontier range states they use laser projection to give an output resolution of 300x600 DPI.

You may be able to find technical details by search for the appropriate patents, although I took a quick look, and couldn't see any.

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