I've been searching the net for a technical explanation of what ISO settings mean in the context of digital cameras but could not find one... yet. Could someone help me by pointing to a few good sources please?

I want to understand what is changed in the camera's algorithm and the way the sensor's photosites are "harvested" when the ISO setting is changed.

I'm interested in the inner workings not the effect on the picture.

Thanks for your help!

Iam Nemo
Physicist

ISO 12232 gives the documment that defines ISO for digital sensors. I believe it costs 75CH. But ISO is changed with sensor gain, not a software solution.

You could also try a search for "Kodak image sensors - ISO measurements." It is based on ISO 12232, but is less detailed. It will give you a hint.

I'm not certain what you mean by "mean" - if you are interested in the "inner workings" rather than the definition of ISO there are some very good sources of information right down to the level of the semiconductor physics.

Just at the moment I forget the very best resource (a paper analysing the differences between CMOS and CCD sensors, IIRC), but I think I found it by following links from

http://clarkvision.com/imagedetail/digital.signal.to.noise/

which of itself is a bit closer to the "effect on the picture" than you may be looking for, but includes some hard facts on the low level practicalities.

Astrophotography resources tend to be good on this stuff, as the image creation and physics knowledge are often reasonably well balanced.

Ken
Physicist

Thanks for the tips. Another ressource worth checking is part of the huge site about microscopy called "Molecular Expressions" and deals with digital imaging. It contains some of the best explanations of CCD technology I've seen, complete with java animations, etc.:

http://micro.magnet.fsu.edu/primer/digitalimaging/index.html

and especially the section:

Concepts in Digital Imaging Technology

It might (or not) contain the answer to my question but it is certainly a good start.

Gotta get back to reading now...

Thanks!
Iam Nemo