How do digital minilabs expose images onto photographic paper?
Asked 6/29/2011
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I’m asking about digital minilabs that print digital files onto traditional silver-halide photographic paper and then process the paper chemically. How is the image actually exposed onto the paper? I assume they do not use a normal video projector, since that likely wouldn’t provide enough resolution or color accuracy. I’ve seen references to systems such as LightJet and Fuji Frontier using lasers. What is the basic technical method these machines use?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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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.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
15y ago
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Generated from our catalog & community — verify before relying on it.
Digital minilabs generally do not use a consumer-style projector that displays the whole image at once. Instead, they typically expose the photographic paper with a laser-based scanning system.
The common idea is that the image is written onto the paper line by line, similar in concept to how a CRT scans across a screen. Because the system is scanning a very small laser spot rather than projecting a fixed pixel grid, resolution is determined mainly by the beam size and the precision of the scanning mechanism.
Community answers also note that Fuji Frontier minilabs specify laser projection, with output around 300×600 dpi. After exposure, the paper is then developed through the normal photographic chemical process used for color photo paper.
So the short answer is: digital minilabs usually form the image by precisely sweeping modulated laser light across the paper, not by using a standard digital projector.
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