Archived posting to the Leica Users Group, 2001/07/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> From: Mxsmanic [mailto:mxsmanic@hotmail.com] > > Austin writes: > > > I believe your premise is flawed. You need to > > sample at slightly more than 2x the maximum frequency > > you want to acquire. A scanner IS a data acquisition > > system. 53 lp/mm is 106 lines/mm, which, as > > you say, is ~2700 SPI. In order to assure that > > the scanner can actually "acquire" all the lines, > > both black and white (which is what a line pair is), > > you would need to sample at > 5400 SPI. > > No. 2700 dpi is sufficient. 2700 samples per inch = 1350 > cycles per inch = > just over 53 cycles (i.e., line pairs) per millimetre. > It turns out that when you measure the available resolution, as opposed to calculating it, the numbers aren't quite that good. The LS-4000 has a theoretical max of 78.74 lp/mm considering purely the sensor density. As I said earlier, the measured resolution of that scanner is around 60 lp/mm. I'd love to have those 18.74 line pairs back, but I won't mourn their passing overmuch - the 60 that are left do a fine real-world job. Paul