Archived posting to the Leica Users Group, 2001/07/31
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]- ----Original Message----- From: darkroom /unix [mailto:darkroom@ix.netcom.com] Sent: Tuesday, July 24, 2001 5:05 PM To: leica-users /unix Cc: darkroom /unix Subject: RE: [Leica] Scanning > Ok, so if as you suggest 2700 dpi is approaching the > do people bother to have drum scans made and why do Nikon bother > to produce > a 4000 dpi scanner? > > Steve 1) Because the premise that 2700 SPI is approaching the limit of film is wrong. 2) Drum scanners do not have the bloom and smear problem that CCD scanners have in the red channel. 3) Drum scanners have a higher dynamic range...both less noise, and an expanded range...but the expanded range is only useful for chrome - ------------------------------------------------------------- I think I'll throw a little curve at you folks. Another factor in determining appropriate scanner resolution may be a phenomenon called "grain alienation", which in my limited understanding is akin to a moire pattern. Grain alienation is an interaction between film grain size and pixel size, and is said to result in exaggerated grain under certain conditions. An introduction to the issue is at this site: http://www.photoscientia.co.uk/Grain.htm My direct experience with the issue is very limited. I've compared drum scans at about 3700 ppi with desktop scans of the same negs at 2700 ppi and observed differences in grain that could be a result of grain alienation. I expect to do some serious testing over the next year as I am gearing up to use digital imaging for permanent preservation of some archival images. (I've been doing scanning for access purposes for many years.) In terms of most real world uses, I am quite happy scanning even Leica-shot (to keep sort of on-topic) transparencies at 2700ppi. It is possible that in certain unusually sharp images there is a loss of very fine detail, but generally speaking it I get very pleasing results that can be enlarged to quite large sizes using technology such as Genuine Fractals. My experience in scanning thousands of archival images is that the limiting factor in image quality is almost always the original image rather than scanner resolution. I make no claim to be an expert on grain alienation, so I encourage those who have time to follow up on this one! Long time lurker, John Poirier Coordinator of Technical Services Northwest Territories Archives Yellowknife, NWT, Canada