What is DMax?

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What is DMax? how is it measured on a scanner? What is a good rating? Can it be related to photographic f/stops? Need information before buying a 1200dpi flatbed w/TMA for scanning film.

-- Dan Harlacher (artlight@teleport.com), October 12, 1999

Answers

It's the maximum reflective or (transmissive) density of the print (or film) the scanner can cope with. Density is measured as the logarithm (base 10) of the light received divided by the light reflected (or transmitted). So a density of 3.0 represents a reclectance (transmission) of 1/1000th of the light, or 0.1%.

I'm not convinced that manufacturers' claims for this statistic can be usefully compared, because the scanner doesn't simply cut off at a particular Dmax. A scanner may be able to distinguish between density 3.8 and pure black, but what does the actual image look like? How noisy is it?

If this is of real concern to you, I suggest you do a comparative test.

-- Alan Gibson (Alan.Gibson@technologist.com), October 13, 1999.


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