Yes, thank you, I omitted film from this chart.
You could add an output magnification factor (a simple multiplication factor) to deal with that.
I believe (right or wrong) that rare documents should be scanned at 600 DPI and saved in a ProPhoto color space. This would be a large file but good as an archive...Yes?
Your criteria only account for theoretical resolution requirements. What is omitted is that a scanner has a native resolution. Using lower resolutions tends to introduce increased (aliasing) artifacts. The aliasing will exaggerate fine detail transitions, e.g. paper structure or sharp edges leading to stairstepping artifacts. From a quality perspective the best results are to be had from scanning at the native scanner resolution, and downsampling with a good resampling method. All other methods will result in sub-optimal results, although for some less critical uses they may be good enough.
Sometimes speed is more important than quality, in which case all bets are off. A compromise can be used in these cases, e.g. scan at twice the required resolution, and downsample to 50%. That will give the best of both worlds.
The required resolution is always a function of the intended end use.
Cheers,
Bart
