Earlier, a couple of posters equated grains in the film emulsion, with digital pixels. That analogyfails on a couple of fronts: First, film grains are not simply "on" or "off;" grains change size, shape and density with exposure, development, etc. Also, unless the film emulsion is so thin that it becomes literally just one grain thick, there will be overlapping grains at various depths through the emulsion; light transmitted through that emulsion will be affected by different grains in different amounts. The result is that the light passing through any point on the film can have any of an infinite range of intensities upon exiting the emulsion.
Digital signals can only take on rigorously defined, discrete values within their range. A stairway has a definite set of elevation changes as you go up or down. You can stand on one tread at a particular height, or go up or down a set amount and stand at the next height, but you can't stand between the set positions of the stair treads.
Analog signals are continuously variable, and can have any conceivable value between the function's minimum and maximum. The comparison to our digital stairway would be a smoothly sloping ramp. The person on the ramp can stop at any height along the way; there are an infinite number of elevation values available.
So, because film can have an infinite number of tones between maximum and minimum, and thus is continuously variable over its range, we choose to call film "analog." It wasn't necessary to use the term "analog" before digital photography came along, but film was then, and is now, storing an analog signal. Film is analog, and that is a correct and accurate use of the term.
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Here are a few definitions of analog (thanks to Google!) from the web:
* Continuous and variable ... waves that represent an infinite number of values. Opposite of analog is digital.
http://largebande.gc.ca/pub/technolo...ictionary.html
* Continuously variable signals or data.
http://www.incredible.co.za/services...y/glossary.asp
* refers to a type of measurement in which the "line of measure" is continuous as compared to one which is discretely incremented.
http://www.notepage.net/wireless-messaging-glossary.htm
* A signal that can take on any value in a range. Contrast with Digital.
http://allinternetnow.com/allnow/ain_terms.htm
* Continuously changing, rather than jumping from one numerical value to the next. See digital.
http://www.mumbaicyber.com/glossary_...ware_micro.asp
* A signal that represents continuously variable information.
http://www.florite.com/support/terminology.htm
* A type of signal ... that takes on a continuous range of values.
http://www.zetex.com/12.0/12-1-3.asp
* Pertaining to measurements or devices in which the output varies continuously. Compare to digital.
http://www.novalynx.com/glossary.html
* An analog or analogue signal is any continuously variable signal. It differs from a digital signal in that small fluctuations in the signal are meaningful. Analog is usually thought of in an electrical context, however mechanical, pneumatic, hydraulic, and other systems may also use analog signals.
http://en.wikipedia.org/wiki/Analog_(signal)
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Originally Posted by Michael Alpert
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