> > On Tue, 20 Apr 2004 17:45:11 -0700, Shel Belinkoff wrote: > > > And what, may I ask, is the problem scanning conventional B&W > > film? > > My understanding is that the problem occurs when you try to use the IR > "scratch & speck removal" systems. Apparently, the silver film grains > react quite differently in those frequency ranges than in the visible > range.
You've got that exactly backwards. IR scratch & dust removal is based on the fact that most film colouring agents are transparent to infra-red, so anything that shows up dark on the IR channel will probably be dust or a scratch. These areas are then filled in by interpolation from surrounding flaw-free areas. Silver blocks IR as well as it blocks visible light, so the automatic cleanup algorithms think all the dark areas of the negative (light areas on the image) need to be interpolated away. In other words, ther problem comes beacuse silver *doesn't* react differently to IR than it does to the visible party of the spectrum.
