Archived posting to the Leica Users Group, 1999/09/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]From: Michael D. Turner <mike@lcl-imaging.com> Sent: Saturday, September 25, 1999 04:20 Subject: [Leica] Re: Low Pressure Sodium > My point in the 2nd paragraph was that even with a > continuous spectrum light source, it is still possible, > in fact, likely, to have too little light recorded > at one end or the other of the spectrum. It's possible, but not very likely, particularly with film (it is more likely to be a problem with digital cameras, if they only use 8-level color). There's always something in there that you can pull out with Photoshop, particularly if you use good 36-bit scans. I've done this from time to time and the noise in the pushed channels hardly changes. In digital photos (at least from consumer cameras), however, there often isn't enough headroom to make this change without making the image a lot noisier. Even then, noisy is often preferable to bright yellow or greenish blue. > Attempting to correct a non-linear bias with a large linear > correction doesn't work. Zero x zero = zero. But it's never zero, just really low. In a 36-bit scan, for example, you can squeeze 256 levels out of the bottom six percent of the intensity range for a channel. That's plenty for quite a large range of applications, including ordinary prints. Gamma can be a problem in the original scan and elsewhere, so you have to be careful about that. -- Anthony