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RE: filmscanners: Scanner resolution (was: BWP seeks scanner)
> Austin Franklin wrote:
> "4000SPI (samples/inch) divided by 25.4 mm/inch = 157.48 samples/mm, which
> means it can always resolve a detail that is (157.48 samples/mm
> divided by 2
> for sampling frequency divided by 2 for line pairs) = 39 lp/mm is the
> MINIMUM resolution that a 4000SPI scanner can resolve. That is for line
> pairs that are perfectly horizontal or vertical."
> Dividing by two *twice* in this calculation is not correct (we've had this
> conversation before).
Sure it is. You even substantiate that below!
> The HIGHEST theoretical resolution that a 4000spi scanner can
> resolve - with
> line pairs that are perfectly horizontal or vertical - is 157.48/2 or 78.7
Read what you wrote first: "The HIGHEST", ie, maximum. Then, read what I
wrote "the MINIMUM". Your "highest" (maximum) is NOT guaranteed resolvable.
Obviously the maximum the scanner can resolve IS the width of the sensor
element in a typical film scanner, which at 4000DPI, that is 4000/25.4/2 or
78.7. Only if the 78.7 lp/mm line up perfectly with a sensor will you
resolve them with the highest contrast.
You have no contrast if the 78.7 lp/mm are off dead on by %50. You will
always get the highest contrast resolving 39 lp/mm, which you are not
guaranteed getting with intermediate values above 39.