Message-Id: <199608161954.OAA25042@library.wustl.edu> Date: Fri, 16 Aug 1996 14:51:55 -0500 From: mailto:huestis@LIBRARY.WUSTL.EDU> Subject: Re: color negatives To: Multiple recipients of list IMAGELIB
On Tue, 30 Jul 1996, Rudolf Gschwind wrote:> >
> >I've been told that NO scanner can successfully scan color negatives. Does
> >anyone have any experience refuting this claim?
> >
> The reason, why scanning of color negatives makes problems, can be explained
> only by photography. Normal color scanners have a spectral
> sensitivity, which matches more or less the visual eye sensitivity, i.e.,
> the peak sensitivities at 450, 560 and 610(!) nm. This gives you good
> results in scanning originals or slides. Color negative material on the other
> hand have color dyes with different absorptions. The "cyan" dye has
> its absorption maximum at 700 nm, i.e. already in the near infrared.
> (consequently, the color negative printing papers are senitized in
> the red to this wavelengths). That means, a color scanner does not
> see "enough" the cyan dye. A second reason is the strong
> orange colored mask of negative materials. This color mask absorbs
> strongly the blue light. The problem is , that the CCD element in the scanner
> has its maximum light sensitivity in the red and NOT in the blue region, i.e.,
> thereis not enough blue light,which makes problems for blue colors.
>
> R. Gschwind (http://foto.chemie.unibas.ch)
>
This post raises an issue which no one has responded to: in scanning, as in any other photographic process, you have your only opportunity to capture as much information as possible. When you adjust color balance after the scan, you are, if anything *subtracting* information. If detail in certain color ranges was not captured because of the color balance of the scanner itself, you can't put this balance back in. Does anyone know if there are scanners which specifically correct this problem by allowing adjustment *before* the scan?A second issue that was raised in other posts was the need to do different color corrections for different negative types. This seems like something that should be "canned", like type-fonts and other printer-setup and driver facilities which we have all come to expect as a standard part of our desktop facilities. Have any software packages produced menus of standard correction values for different film types? If not, it seems that this group would be a suitable place for people who have figured things out by trial and error to pool their knowledge into a FAQ.
Jeff Huestis Washington University Libraries St. Louis, Missouri 314-935-5951 http://library.wustl.edu/~huestis