Archived posting to the Leica Users Group, 2000/07/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Wed, 19 Jul 2000 10:20:01, "Rob Studdert" <audiob@ozemail.com.au> wrote: > On 19 Jul 2000, at 8:44, Peter Zak wrote: >> When I examine the slides under a loupe or with a projector I see >> much that the scanner is simply failing to pick up. I notice this >> most with Kodacrome 25 and Velvia - I've been advised by the local >> Nikon service techos to turn the Nikon colour management off when >> scanning Kodachrome. > Don't expect any 2700 or 4000dpi scanner to come close to resolving > all the detail contained Kodacrome 25 and Velvia, you need about > 6800dpi to even get close. A good approximation for conversion from film terms to dpi is 1lp/mm = 100dpi (24bit color or 16bit b&w), so to capture a "typical" film image with 80lp/mm detail, you'd need about 8000dpi. Of course, both 50mm 'cron and Velvia have much better resolution than this, so if you wanted a full information scan, you'd probably need about 12000dpi. The calculation goes like this: 1lp/mm * ~25mm/in * 2lines/lp * 2dots/line = 100dpi The 2dots/line is a factor similar to the Nyquist ratio for digital audio. You need to sample at half the size of the smallest feature you expect to capture. Regards, Ross - -- Ross Bagley & Associates http://rossbagley.com/rba "We don't just write software, we help you write software better!"